Method for reporting channel state information in wireless communication system and device therefor

ABSTRACT

A method for reporting, by a user equipment (UE), channel state information (CSI) in a wireless communication system, includes transmitting, to a base station, UE capability information including information for a maximum number of channel state information-reference signal (CSI-RS) resources; receiving, from the base station, CSI-RS configuration information via a higher layer signaling; receiving, from the base station, a channel state information-reference signal (CSI-RS) on at least one CSI-RS port based on the CSI-RS configuration information; measuring a channel based on the CSI-RS; and reporting, to the base station, a result of the channel measurement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/565,081, filed on Oct. 6, 2017, which is the National Phase of PCTInternational Application No. PCT/KR2016/003780, filed on Apr. 11, 2016,which claims priority under 35 U.S.C. 119(e) to U.S. ProvisionalApplication Nos. 62/145,654 filed on Apr. 10, 2015, 62/204,967 filed onAug. 13, 2015, 62/205,657 filed on Aug. 14, 2015, 62/208,808 filed onAug. 23, 2015, 62/211,007 filed on Aug. 28, 2015, 62/238,707 filed onOct. 8, 2015, 62/251,650 filed on Nov. 5, 2015, 62/297,083 filed on Feb.18, 2016 and 62/297,157 filed on Feb. 19, 2016, all of which are herebyexpressly incorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method for reporting channel state information(CSI) based on a reference signal by a UE and a device for supportingthe same.

Discussion of the Related Art

Mobile communication systems have been developed to provide voiceservices while ensuring the activity of a user. However, the mobilecommunication systems have been expanded to their regions up to dataservices as well as voice. Today, the shortage of resources is causeddue to an explosive increase of traffic, and more advanced mobilecommunication systems are required due to user's need for higher speedservices.

Requirements for a next-generation mobile communication system basicallyinclude the acceptance of explosive data traffic, a significant increaseof a transfer rate per user, the acceptance of the number ofsignificantly increased connection devices, very low end-to-end latency,and high energy efficiency. To this end, research is carried out onvarious technologies, such as dual connectivity, massive Multiple InputMultiple Output (MIMO), in-band full duplex, Non-Orthogonal MultipleAccess (NOMA), the support of a super wideband, and device networking.The present specification has been made in an effort to provide a methodfor transmitting/receiving terminal capability information including themaximum number of CSI-RS ports supported by a terminal in a specific CSIreporting type or class.

SUMMARY OF THE INVENTION

Further, the present specification has been made in an effort to providea method for transmitting/receiving UE capability information includingthe maximum number of CSI-RS resources supported by a UE in a specificCSI reporting type or class.

In addition, the present specification has been made in an effort toprovide a method for transmitting/receiving UE capability informationincluding the number of CSI-RS port numbers supported for each CSI-RSresource in a specific CSI reporting type or class.

Moreover, the present specification has been made in an effort toprovide a method for individually and independently transmittinginformation on the maximum number of CSI-RS resources and information onthe number of CSI-RS ports supported for each CSI-RS resource.

Further, the present specification has been made in an effort to providea method for transmitting/receiving UE capability information includingcodebook configuration information supported by a UE in a specific CSIreporting type or class.

In addition, the present specification has been made in an effort toprovide a method for transmitting/receiving UE capability informationincluding an SRS transmission type and/or a measurement restriction typesupported by a UE in a specific CSI reporting type or class.

Moreover, the present specification has been made in an effort toprovide a method for transmitting/receiving UE capability informationincluding specific CSI reporting type information supported by a UE.

The technical objects of the present invention are not limited to theaforementioned technical objects, and other technical objects, which arenot mentioned above, will be apparently appreciated by a person havingordinary skill in the art from the following description.

Technical Solution

According to the present specification, a method for reporting channelstate information (CSI) in a wireless communication system, which isperformed by a UE includes: transmitting UE capability informationincluding second control information indicating the total number ofCSI-RS resources which are maximally supported in one CSI process to abase station; receiving CSI process related information including CSI-RSconfiguration information from the base station through high layersignaling; receiving at least one CSI-RS from the base station based onthe received CSI process related information, the at least one CSI-RSbeing transmitted through at least one CSI-RS port of the base station;measuring a channel for the at least one CSI-RS port based on the atleast received CSI-RS; and reporting the channel measurement result tothe base station.

Further, in the present specification, the method further includestransmitting to the base station third control information representingthe total number of CSI-RS ports maximally supported for each CSI-RSresource.

In addition, in the present specification, the third control informationis included in the UE capability information.

Moreover, in the present specification, the UE capability informationfurther includes first control information representing the total numberof CSI-RS ports maximally supported in the one CSI process.

Further, in the present specification, the UE capability informationfurther includes CSI reporting type information representing a CSIreporting type supported by the UE.

In addition, in the present specification, the CSI reporting typeinformation includes at least one of a first type indicating anon-precoded CSI-RS based CSI reporting operation and a second typeindicating a beamformed CSI-RS based CSI reporting operation.

Moreover, in the present specification, the first type is Class A, andthe second type is Class B.

Further, in the present specification, when the CSI reporting typeinformation is configured to the second type, the second controlinformation is included in the UE capability information.

Moreover, in the present specification, a maximum value of the secondcontrol information is 8.

In addition, in the present specification, the second controlinformation is configured to be the same as each other or different fromeach other for each CSI process.

Further, in the present specification, the CSI process relatedinformation further includes type indication information indicating aCSI reporting type to be performed by the UE.

Further, according to the present specification, a UE for reportingchannel state information (CSI) in a wireless communication systemincludes: a radio frequency (RF) unit for transmitting and receiving aradio signal; and a processor controlling the RF unit, and the processorcontrols to transmit UE capability information including second controlinformation representing the total number of CSI-RS resources which aremaximally supported in one CSI process to a base station, receive CSIprocess related information including CSI-RS configuration informationfrom the base station through high layer signaling, receive at least oneCSI-RS from the base station based on the received CSI process relatedinformation, the at least one CSI-RS being transmitted through at leastone CSI-RS port of the base station, measure a channel for the at leastone CSI-RS port based on the at least received CSI-RS, and report thechannel measurement result to the base station.

In addition, in the present specification, the processor controls thirdcontrol information indicating the total number of CSI-RS portsmaximally supported for each CSI-RS resource to be transmitted to thebase station.

In the present specification, a CSI operation related parameter whichmay be supported by a UE, and the like are transmitted while beingincluded in UE capability information, and as a result, a base stationconfigures the CSI operation related parameter, and the like for the UEto reduce complexity of UE implementation.

Effects which can be obtained in the present invention are not limitedto the aforementioned effects and other unmentioned effects will beclearly understood by those skilled in the art from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included a part of thisspecification to provide a further understanding of this document,provide embodiments of the present invention and together with thedetailed description serve to explain the technical characteristics ofthe present invention.

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 5 shows the configuration of a known multi-input multi-output(MIMO) antenna communication system.

FIG. 6 is a diagram illustrating channels from a plurality oftransmission antennas to a single reception antenna.

FIG. 7 shows an example of component carriers and a componentaggregation in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 8 is a diagram for illustrating a contention-based random accessprocedure in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 9 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 10 is a diagram illustrating a CSI-RS configuration in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 11 illustrates a system having a plurality oftransmission/reception antennas through which an eNB or a UE is capableof three-dimensional (3-D) beamforming based on an AAS in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 12 illustrates RSRP for each antenna port of an RRM-RS according toan embodiment of the present invention.

FIG. 13 illustrates RRM-RS antenna port grouping levels according to anembodiment of the present invention.

FIG. 14 is a diagram illustrating antenna ports and antenna port groupsof RRM-RSs arrayed in 2-D indices according to an embodiment of thepresent invention.

FIG. 15 is a diagram illustrating one example of a polarization based 2Dplanar array model.

FIG. 16 is a diagram illustrating one example of a transceiver units(TXRUs) model.

FIG. 17 is a diagram for describing a basic concept of codebook basedprecoding.

FIG. 18 is a diagram illustrating one example of a method for measuringand reporting CSI.

FIG. 19 is a diagram illustrating another example of the method formeasuring and reporting CSI.

FIG. 20 is a diagram illustrating yet another example of the method formeasuring and reporting CSI.

FIG. 21 is a diagram illustrating one example of 6 DB RS power boostingfor a frequency division multiplexed (FDM) RS.

FIG. 22 is a flowchart illustrating one example of a UE capabilityinformation signaling method proposed by the present specification.

FIG. 23 is a flowchart illustrating another example of the UE capabilityinformation signaling method proposed by the present specification.

FIG. 24 is a flowchart illustrating yet another example of the UEcapability information signaling method proposed by the presentspecification.

FIG. 25 illustrates one example of an 8-port CSI-RS pattern in anexisting PRB pair.

FIG. 26 is a diagram illustrating one example of a 2D-AAS antennaconfiguration.

FIG. 27 is a diagram illustrating one example of the 2D-AAS antennaconfiguration for a potential CSI-RS configuration.

FIG. 28 illustrates one example of a partial CSI-RS pattern for 16cross-pole antenna elements.

FIG. 29 is a diagram illustrating one example for finding a verticaldirection in a cell.

FIG. 30 is a diagram illustrating one example of concurrent CSI-RStransmission having multiple virtual matrixes.

FIG. 31 illustrates one example of a method for designing 12 portnon-precoded CSI-RS patterns in (a), and illustrates one example of amethod for designing 16 port non-precoded CSI-RS patterns in (b).

FIG. 32 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Adetailed description to be disclosed hereinbelow together with theaccompanying drawing is to describe embodiments of the present inventionand not to describe a unique embodiment for carrying out the presentinvention. The detailed description below includes details in order toprovide a complete understanding. However, those skilled in the art knowthat the present invention can be carried out without the details.

In some cases, in order to prevent a concept of the present inventionfrom being ambiguous, known structures and devices may be omitted or maybe illustrated in a block diagram format based on core function of eachstructure and device.

In the specification, a base station means a terminal node of a networkdirectly performing communication with a terminal. In the presentdocument, specific operations described to be performed by the basestation may be performed by an upper node of the base station in somecases. That is, it is apparent that in the network constituted bymultiple network nodes including the base station, various operationsperformed for communication with the terminal may be performed by thebase station or other network nodes other than the base station. A basestation (BS) may be generally substituted with terms such as a fixedstation, Node B, evolved-NodeB (eNB), a base transceiver system (BTS),an access point (AP), and the like. Further, a ‘terminal’ may be fixedor movable and be substituted with terms such as user equipment (UE), amobile station (MS), a user terminal (UT), a mobile subscriber station(MSS), a subscriber station (SS), an advanced mobile station (AMS), awireless terminal (WT), a Machine-Type Communication (MTC) device, aMachine-to-Machine (M2M) device, a Device-to-Device (D2D) device, andthe like.

Hereinafter, a downlink means communication from the base station to theterminal and an uplink means communication from the terminal to the basestation. In the downlink, a transmitter may be a part of the basestation and a receiver may be a part of the terminal. In the uplink, thetransmitter may be a part of the terminal and the receiver may be a partof the base station.

Specific terms used in the following description are provided to helpappreciating the present invention and the use of the specific terms maybe modified into other forms within the scope without departing from thetechnical spirit of the present invention.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), non-orthogonal multiple access (NOMA), and the like. The CDMAmay be implemented by radio technology universal terrestrial radioaccess (UTRA) or CDMA2000. The TDMA may be implemented by radiotechnology such as Global System for Mobile communications (GSM)/GeneralPacket Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution(EDGE). The OFDMA may be implemented as radio technology such as IEEE802.11(Wi-Fi), IEEE 802.16(WiMAX), IEEE 802-20, E-UTRA (Evolved UTRA),and the like. The UTRA is a part of a universal mobile telecommunicationsystem (UMTS). 3rd generation partnership project (3GPP) long termevolution (LTE) as a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) adopts the OFDMA in a downlink and theSC-FDMA in an uplink. LTE-advanced (A) is an evolution of the 3GPP LTE.

The embodiments of the present invention may be based on standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2 whichare the wireless access systems. That is, steps or parts which are notdescribed to definitely show the technical spirit of the presentinvention among the embodiments of the present invention may be based onthe documents. Further, all terms disclosed in the document may bedescribed by the standard document.

3GPP LTE/LTE-A is primarily described for clear description, buttechnical features of the present invention are not limited thereto.

General Wireless Communication System to which an Embodiment of thePresent Invention May be Applied

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

3GPP LTE/LTE-A support a type 1 radio frame structure capable of beingapplied to frequency division duplex (FDD) and a type 2 radio framestructure capable of being applied to time division duplex (TDD).

In FIG. 1, the size of the radio frame in a time domain is expressed ina multiple of a time unit “T_s=1/(15000*2048).” Downlink and uplinktransmission includes a radio frame having an interval ofT_f=307200*T_s=10 ms.

FIG. 1(a) illustrates the type 1 radio frame structure. The type 1 radioframe may be applied to both full duplex FDD and half duplex FDD.

The radio frame includes 10 subframes. One radio frame includes 20 slotseach having a length of T_slot=15360*T_s=0.5 ms. Indices 0 to 19 areassigned to the respective slots. One subframe includes two contiguousslots in the time domain, and a subframe i includes a slot 2 i and aslot 2 i+1. The time taken to send one subframe is called a transmissiontime interval (TTI). For example, the length of one subframe may be 1ms, and the length of one slot may be 0.5 ms.

In FDD, uplink transmission and downlink transmission are classified inthe frequency domain. There is no restriction to full duplex FDD,whereas a UE is unable to perform transmission and reception at the sametime in a half duplex FDD operation.

One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in the time domain and includes a pluralityof resource blocks (RBs) in the frequency domain. An OFDM symbol is forexpressing one symbol period because 3GPP LTE uses OFDMA in downlink.The OFDM symbol may also be called an SC-FDMA symbol or a symbol period.The resource block is a resource allocation unit and includes aplurality of contiguous subcarriers in one slot.

FIG. 1(b) shows the type 2 radio frame structure.

The type 2 radio frame structure includes 2 half frames each having alength of 153600*T_s=5 ms. Each of the half frames includes 5 subframeseach having a length of 30720*T_s=1 ms.

In the type 2 radio frame structure of a TDD system, an uplink-downlinkconfiguration is a rule showing how uplink and downlink are allocated(or reserved) with respect to all of subframes.

Table 1 shows the uplink-downlink configuration.

TABLE 1 Downlink- to-Uplink Uplink- Switch- Downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

Referring to Table 1, “D” indicates a subframe for downlinktransmission, “U” indicates a subframe for uplink transmission, and “S”indicates a special subframe including the three fields of a downlinkpilot time slot (DwPTS), a guard period (GP), and an uplink pilot timeslot (UpPTS) for each of the subframes of the radio frame.

The DwPTS is used for initial cell search, synchronization or channelestimation by a UE. The UpPTS is used for an eNB to perform channelestimation and for a UE to perform uplink transmission synchronization.The GP is an interval for removing interference occurring in uplink dueto the multi-path delay of a downlink signal between uplink anddownlink.

Each subframe i includes the slot 2 i and the slot 2 i+1 each having“T_slot=15360*T_s=0.5 ms.”

The uplink-downlink configuration may be divided into seven types. Thelocation and/or number of downlink subframes, special subframes, anduplink subframes are different in the seven types.

A point of time changed from downlink to uplink or a point of timechanged from uplink to downlink is called a switching point.Switch-point periodicity means a cycle in which a form in which anuplink subframe and a downlink subframe switch is repeated in the samemanner. The switch-point periodicity supports both 5 ms and 10 ms. Inthe case of a cycle of the 5 ms downlink-uplink switching point, thespecial subframe S is present in each half frame. In the case of thecycle of the 5 ms downlink-uplink switching point, the special subframeS is present only in the first half frame.

In all of the seven configurations, No. 0 and No. 5 subframes and DwPTSsare an interval for only downlink transmission. The UpPTSs, thesubframes, and a subframe subsequent to the subframes are always aninterval for uplink transmission.

Both an eNB and a UE may be aware of such uplink-downlink configurationsas system information. The eNB may notify the UE of a change in theuplink-downlink allocation state of a radio frame by sending only theindex of configuration information whenever uplink-downlinkconfiguration information is changed. Furthermore, the configurationinformation is a kind of downlink control information. Like schedulinginformation, the configuration information may be transmitted through aphysical downlink control channel (PDCCH) and may be transmitted to allof UEs within a cell in common through a broadcast channel as broadcastinformation.

Table 2 shows a configuration (i.e., the length of a DwPTS/GP/UpPTS) ofthe special subframe.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix in UpPTSdownlink Normal UpPTS cyclic Extended Normal Extended Special prefixcyclic cyclic cyclic subframe in prefix prefix in prefix inconfiguration DwPTS uplink in uplink DwPTS uplink uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The structure of the radio frame according to the example of FIG. 1 isonly one example. The number of subcarriers included in one radio frame,the number of slots included in one subframe, and the number of OFDMsymbols included in one slot may be changed in various manners.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin the wireless communication system to which the present invention canbe applied.

Referring to FIG. 2, one downlink slot includes the plurality of OFDMsymbols in the time domain. Herein, it is exemplarily described that onedownlink slot includes 7 OFDM symbols and one resource block includes 12subcarriers in the frequency domain, but the present invention is notlimited thereto.

Each element on the resource grid is referred to as a resource elementand one resource block includes 12×7 resource elements. The number ofresource blocks included in the downlink slot, NDL is subordinated to adownlink transmission bandwidth.

A structure of the uplink slot may be the same as that of the downlinkslot.

FIG. 3 illustrates a structure of a downlink subframe in the wirelesscommunication system to which the present invention can be applied.

Referring to FIG. 3, a maximum of three former OFDM symbols in the firstslot of the sub frame is a control region to which control channels areallocated and residual OFDM symbols is a data region to which a physicaldownlink shared channel (PDSCH) is allocated. Examples of the downlinkcontrol channel used in the 3GPP LTE include a Physical Control FormatIndicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH),a Physical Hybrid-ARQ Indicator Channel (PHICH), and the like.

The PFCICH is transmitted in the first OFDM symbol of the subframe andtransports information on the number (that is, the size of the controlregion) of OFDM symbols used for transmitting the control channels inthe subframe. The PHICH which is a response channel to the uplinktransports an Acknowledgement (ACK)/Not-Acknowledgement (NACK) signalfor a hybrid automatic repeat request (HARD). Control informationtransmitted through a PDCCH is referred to as downlink controlinformation (DCI). The downlink control information includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for apredetermined terminal group.

The PDCCH may transport A resource allocation and transmission format(also referred to as a downlink grant) of a downlink shared channel(DL-SCH), resource allocation information (also referred to as an uplinkgrant) of an uplink shared channel (UL-SCH), paging information in apaging channel (PCH), system information in the DL-SCH, resourceallocation for an upper-layer control message such as a random accessresponse transmitted in the PDSCH, an aggregate of transmission powercontrol commands for individual terminals in the predetermined terminalgroup, a voice over IP (VoIP). A plurality of PDCCHs may be transmittedin the control region and the terminal may monitor the plurality ofPDCCHs. The PDCCH is constituted by one or an aggregate of a pluralityof continuous control channel elements (CCEs). The CCE is a logicalallocation wise used to provide a coding rate depending on a state of aradio channel to the PDCCH. The CCEs correspond to a plurality ofresource element groups. A format of the PDCCH and a bit number ofusable PDCCH are determined according to an association between thenumber of CCEs and the coding rate provided by the CCEs.

The base station determines the PDCCH format according to the DCI to betransmitted and attaches the control information to a cyclic redundancycheck (CRC) to the control information. The CRC is masked with a uniqueidentifier (referred to as a radio network temporary identifier (RNTI))according to an owner or a purpose of the PDCCH. In the case of a PDCCHfor a specific terminal, the unique identifier of the terminal, forexample, a cell-RNTI (C-RNTI) may be masked with the CRC. Alternatively,in the case of a PDCCH for the paging message, a paging indicationidentifier, for example, the CRC may be masked with a paging-RNTI(P-RNTI). In the case of a PDCCH for the system information, in moredetail, a system information block (SIB), the CRC may be masked with asystem information identifier, that is, a system information (SI)-RNTI.The CRC may be masked with a random access (RA)-RNTI in order toindicate the random access response which is a response to transmissionof a random access preamble.

FIG. 4 illustrates a structure of an uplink subframe in the wirelesscommunication system to which the present invention can be applied.

Referring to FIG. 4, the uplink subframe may be divided into the controlregion and the data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) transporting uplink control information isallocated to the control region. A physical uplink shared channel(PUSCH) transporting user data is allocated to the data region. Oneterminal does not simultaneously transmit the PUCCH and the PUSCH inorder to maintain a single carrier characteristic.

A resource block (RB) pair in the subframe are allocated to the PUCCHfor one terminal. RBs included in the RB pair occupy differentsubcarriers in two slots, respectively. The RB pair allocated to thePUCCH frequency-hops in a slot boundary.

Multi-Input Multi-Output (MIMO)

An MIMO technology uses multiple transmitting (Tx) antennas and multiplereceiving (Rx) antennas by breaking from generally one transmittingantenna and one receiving antenna up to now. In other words, the MIMOtechnology is a technology for achieving capacity increment orcapability enhancement by using a multiple input multiple output antennaat a transmitter side or a receiver side of the wireless communicationsystem. Hereinafter, “MIMO” will be referred to as “multiple inputmultiple output antenna”.

More specifically, the MIMO technology does not depend on one antennapath in order to receive one total message and completes total data bycollecting a plurality of data pieces received through multipleantennas. Consequently, the MIMO technology may increase a data transferrate within in a specific system range and further, increase the systemrange through a specific data transfer rate.

In next-generation mobile communication, since a still higher datatransfer rate than the existing mobile communication is required, it isanticipated that an efficient multiple input multiple output technologyis particularly required. In such a situation, an MIMO communicationtechnology is a next-generation mobile communication technology whichmay be widely used in a mobile communication terminal and a relay andattracts a concern as a technology to overcome a limit of a transmissionamount of another mobile communication according to a limit situationdue to data communication extension, and the like.

Meanwhile, the multiple input multiple output (MIMO) technology amongvarious transmission efficiency improvement technologies which have beenresearched in recent years as a method that may epochally improve acommunication capacity and transmission and reception performancewithout additional frequency allocation or power increment has thelargest attention in recent years.

FIG. 5 is a configuration diagram of a general multiple input multipleoutput (MIMO) communication system.

Referring to FIG. 5, when the number of transmitting antennas increasesto NT and the number of receiving antennas increases to NR at the sametime, since a theoretical channel transmission capacity increases inproportion to the number of antennas unlike a case using multipleantennas only in a transmitter or a receiver, a transfer rate may beimproved and frequency efficiency may be epochally improved. In thiscase, the transfer rate depending on an increase in channel transmissioncapacity may theoretically increase to a value acquired by multiplying amaximum transfer rate (Ro) in the case using one antenna by a rateincrease rate (Ri) given below.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, for example, in an MIMO communication system using fourtransmitting antennas and four receiving antennas, a transfer rate whichis four times higher than a single antenna system may be acquired.

Such an MIMO antenna technology may be divided into a spatial diversityscheme increasing transmission reliability by using symbols passingthrough various channel paths and a spatial multiplexing schemeimproving the transfer rate by simultaneously transmitting multiple datasymbols by using multiple transmitting antennas. Further, a researchinto a scheme that intends to appropriately acquire respectiveadvantages by appropriately combining two schemes is also a field whichhas been researched in recent years.

The respective schemes will be described below in more detail.

First, the spatial diversity scheme includes a space-time block codingseries and a space-time Trelis coding series scheme simultaneously usinga diversity gain and a coding gain. In general, the Trelis is excellentin bit error rate enhancement performance and code generation degree offreedom, but the space-time block code is simple in operationalcomplexity. In the case of such a spatial diversity gain, an amountcorresponding to a multiple (NT×NR) of the number (NT) of transmittingantennas and the number (NR) of receiving antennas may be acquired.

Second, the spatial multiplexing technique is a method that transmitsdifferent data arrays in the respective transmitting antennas and inthis case, mutual interference occurs among data simultaneouslytransmitted from the transmitter in the receiver. The receiver receivesthe data after removing the interference by using an appropriate signalprocessing technique. A noise removing scheme used herein includes amaximum likelihood detection (MLD) receiver, a zero-forcing (ZF)receiver, a minimum mean square error (MMSE) receiver, a diagonal-belllaboratories layered space-time (D-BLAST), a vertical-bell laboratorieslayered space-time), and the like and in particular, when channelinformation may be known in the transmitter side, a singular valuedecomposition (SVD) scheme, and the like may be used.

Third, a technique combining the space diversity and the spatialmultiplexing may be provided. When only the spatial diversity gain isacquired, the performance enhancement gain depending on an increase indiversity degree is gradually saturated and when only the spatialmultiplexing gain is acquired, the transmission reliability deterioratesin the radio channel. Schemes that acquire both two gains while solvingthe problem have been researched and the schemes include a space-timeblock code (Double-STTD), a space-time BICM (STBICM), and the like.

In order to describe a communication method in the MIMO antenna systemdescribed above by a more detailed method, when the communication methodis mathematically modeled, the mathematical modeling may be shown asbelow.

First, it is assumed that NT transmitting antennas and NR receivingantennas are present as illustrated in FIG. 5.

First, in respect to a transmission signal, when NT transmittingantennas are provided, NT may be expressed as a vector given belowbecause the maximum number of transmittable information is NT.s=└s ₁ ,s ₂ ,Λ,s _(N) _(T) ┘^(T)  [Equation 2]

Transmission power may be different in the respective transmissioninformation s1, s2, sNT and in this case, when the respectivetransmission power is P1, P2, PNT, the transmission information of whichthe transmission power is adjusted may be expressed as a vector givenbelow.ŝ=[ŝ ₁ ,ŝ ₂ ,Λ,ŝ _(N) _(T) ]^(T)=[P ₁ s ₁ ,P ₂ s ₂ ,Λ,P _(N) _(T) s _(N)_(T) ]^(T)  [Equation 3]

Further, ŝ may be expressed as described below as a diagonal matrix P ofthe transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & O & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\M \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

The information vector ŝ of which the transmission power is adjusted ismultiplied by a weight matrix W to constitute NT transmission signalsx1, x2, . . . , xNT which are actually transmitted. Herein, the weightmatrix serves to appropriately distribute the transmission informationto the respective antennas according to a transmission channelsituation, and the like. The transmission signals x1, x2, . . . , xNTmay be expressed as below by using a vector x.

$\begin{matrix}{x = {\quad{\begin{bmatrix}x_{1} \\x_{2} \\M \\x_{i} \\M \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{11} & \Lambda & w_{1N_{T}} \\w_{21} & w_{22} & \Lambda & w_{2N_{T}} \\M & \; & O & \; \\w_{i\; 1} & w_{i\; 2} & \Lambda & w_{{iN}_{T}} \\M & \; & O & \; \\w_{N_{T}1} & w_{N_{T}2} & \Lambda & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\M \\{\hat{s}}_{j} \\M \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, wij represents a weight between the i-th transmittingantenna and j-th transmission information and W represents the weight asthe matrix. The matrix W is called a weight matrix or a precodingmatrix.

The transmission signal x described above may be divided intotransmission signals in a case using the spatial diversity and a caseusing the spatial multiplexing.

In the case using the spatial multiplexing, since different signals aremultiplexed and sent, all elements of an information vector s havedifferent values, while when the spatial diversity is used, since thesame signal is sent through multiple channel paths, all of the elementsof the information vector s have the same value.

A method mixing the spatial multiplexing and the spatial diversity mayalso be considered. That is, for example, a case may also be consideredin which the same signal is transmitted using the spatial diversitythrough three transmitting antennas and different signals are sent byspatial multiplexing through residual transmitting antennas.

Next, when NR receiving antennas are provided, received signals y1, y2,. . . , yNR of the respective antennas are expressed as a vector y asdescribed below.y=[y ₁ ,y ₂ ,Λ,y _(N) _(R) ]^(T)  [Equation 6]

If channels are modeled in the MIMO antenna communication system, thechannels may be distinguished based on transmitting and receivingantenna indexes and a channel passing through a receiving antenna i froma transmitting antenna j will be represented as hij. Herein, it is notedthat in the case of the order of the index of hij, the receiving antennaindex is earlier and the transmitting antenna index is later.

The multiple channels are gathered into one to be expressed even asvector and matrix forms. An example of expression of the vector will bedescribed below.

FIG. 6 is a diagram illustrating a channel from multiple transmittingantennas to one receiving antenna.

As illustrated in FIG. 6, a channel which reaches receiving antenna Ifrom a total of NT transmitting antennas may be expressed as below.h _(i) ^(T) =└h _(i1) ,h _(i2) ,Λ,h _(iN) _(T) ┘  [Equation 7]

Further, all of channels passing through NR receiving antennas from NTtransmitting antennas may be shown as below through matrix expressionshown in Equation given above.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\M \\h_{i}^{T} \\M \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \Lambda & h_{1N_{T}} \\h_{21} & h_{22} & \Lambda & h_{2N_{T}} \\M & \; & O & \; \\h_{i\; 1} & h_{i\; 2} & \Lambda & h_{{iN}_{T}} \\M & \; & O & \; \\h_{N_{R}1} & h_{N_{R}2} & \Lambda & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Since additive white Gaussian noise (AWGN) is added after passingthrough a channel matrix H given above in an actual channel, whitenoises n1, n2, . . . , nNR added to NR receiving antennas, respectivelyare expressed as below.n=[n ₁ ,n ₂ ,Λ,n _(N) _(R) ]^(T)  [Equation 9]

Each of the transmission signal, the reception signal, the channel, andthe white noise in the MIMO antenna communication system may beexpressed through a relationship given below by modeling thetransmission signal, the reception signal, the channel, and the whitenoise.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\M \\y_{i} \\M \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \Lambda & h_{1N_{T}} \\h_{21} & h_{22} & \Lambda & h_{2N_{T}} \\M & \; & O & \; \\h_{i\; 1} & h_{i\; 2} & \Lambda & h_{{iN}_{T}} \\M & \; & O & \; \\h_{N_{R}1} & h_{N_{R}2} & \Lambda & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\M \\x_{j} \\M \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\M \\n_{i} \\M \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

The number of rows and columns of the channel matrix H representing thestate of the channel is determined by the number of transmitting andreceiving antennas. In the case of the channel matrix H, the number ofrows becomes equivalent to NR which is the number of receiving antennasand the number of columns becomes equivalent to NR which is the numberof transmitting antennas. That is, the channel matrix H becomes an NR×NRmatrix.

In general, a rank of the matrix is defined as the minimum number amongthe numbers of independent rows or columns. Therefore, the rank of thematrix may not be larger than the number of rows or columns. As anequation type example, the rank (rank(H)) of the channel matrix H islimited as below.rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

Further, when the matrix is subjected to Eigen value decomposition, therank may be defined as not 0 but the number of Eigen values among theEigen values. By a similar method, when the rank is subjected tosingular value decomposition, the rank may be defined as not 0 but thenumber of singular values. Accordingly, a physical meaning of the rankin the channel matrix may be the maximum number which may send differentinformation in a given channel.

In this specification, a ‘rank’ for MIMO transmission represents thenumber of paths to independently transmit the signal at a specific timeand in a specific frequency resource and ‘the number of layers’represents the number of signal streams transmitted through each path.In general, since the transmitter side transmits layers of the numbercorresponding to the number of ranks used for transmitting the signal,the rank has the same meaning as the number layers if not particularlymentioned.

Carrier Aggregation

A communication environment considered in embodiments of the presentinvention includes multi-carrier supporting environments. That is, amulti-carrier system or a carrier aggregation system used in the presentinvention means a system that aggregates and uses one or more componentcarriers (CCs) having a smaller bandwidth smaller than a target band atthe time of configuring a target wideband in order to support awideband.

In the present invention, a multi-carrier means an aggregation ofcarriers (alternatively carrier aggregation). In this case, theaggregation of carriers means both an aggregation between continuouscarriers and an aggregation between non-contiguous carriers. Further,the number of component carriers aggregated between downlink and uplinkmay be differently set. A case where the number of downlink componentcarriers (hereinafter referred to as a “DL CC”) and the number of uplinkcomponent carriers (hereinafter, referred to as an “UL CC”) are the sameis referred to as a “symmetric aggregation”, and a case where the numberof downlink component carriers and the number of uplink componentcarriers are different is referred to as an “asymmetric aggregation.”The carrier aggregation may be used interchangeably with a term, such asa bandwidth aggregation or a spectrum aggregation.

A carrier aggregation configured by combining two or more componentcarriers aims at supporting up to a bandwidth of 100 MHz in the LTE-Asystem. When one or more carriers having the bandwidth than the targetband are combined, the bandwidth of the carriers to be combined may belimited to a bandwidth used in the existing system in order to maintainbackward compatibility with the existing IMT system. For example, theexisting 3GPP LTE system supports bandwidths of 1.4, 3, 5, 10, 15, and20 MHz and a 3GPP LTE-advanced system (that is, LTE-A) may be configuredto support a bandwidth larger than 20 MHz by using on the bandwidth forcompatibility with the existing system. Further, the carrier aggregationsystem used in the preset invention may be configured to support thecarrier aggregation by defining a new bandwidth regardless of thebandwidth used in the existing system.

The LTE-A system uses a concept of the cell in order to manage a radioresource.

The carrier aggregation environment may be called a multi-cellenvironment. The cell is defined as a combination of a pair of adownlink resource (DL CC) and an uplink resource (UL CC), but the uplinkresource is not required. Therefore, the cell may be constituted by onlythe downlink resource or both the downlink resource and the uplinkresource. When a specific terminal has only one configured serving cell,the cell may have one DL CC and one UL CC, but when the specificterminal has two or more configured serving cells, the cell has DL CCsas many as the cells and the number of UL CCs may be equal to or smallerthan the number of DL CCs.

Alternatively, contrary to this, the DL CC and the UL CC may beconfigured. That is, when the specific terminal has multiple configuredserving cells, a carrier aggregation environment having UL CCs more thanDL CCs may also be supported. That is, the carrier aggregation may beappreciated as aggregation of two or more cells having different carrierfrequencies (center frequencies). Herein, the described ‘cell’ needs tobe distinguished from a cell as an area covered by the base stationwhich is generally used.

The cell used in the LTE-A system includes a primary cell (PCell) and asecondary cell (SCell. The P cell and the S cell may be used as theserving cell. In a terminal which is in an RRC_CONNECTED state, but doesnot have the configured carrier aggregation or does not support thecarrier aggregation, only one serving constituted by only the P cell ispresent. On the contrary, in a terminal which is in the RRC_CONNECTEDstate and has the configured carrier aggregation, one or more servingcells may be present and the P cell and one or more S cells are includedin all serving cells.

The serving cell (P cell or S cell) may be configured through an RRCparameter. PhysCellld as a physical layer identifier of the cell hasinteger values of 0 to 503. SCellIndex as a short identifier used toidentify the S cell has integer values of 1 to 7. ServCellIndex as ashort identifier used to identify the serving cell (P cell or S cell)has the integer values of 0 to 7. The value of 0 is applied to the Pcell and SCellIndex is previously granted for application to the S cell.That is, a cell having a smallest cell ID (alternatively, cell index) inServCellIndex becomes the P cell.

The P cell means a cell that operates on a primary frequency(alternatively a primary CC). The terminal may be used to perform aninitial connection establishment process or a connectionre-establishment process and may be designated as a cell indicatedduring a handover process. Further, the P cell means a cell whichbecomes the center of control associated communication among servingcells configured in the carrier aggregation environment. That is, theterminal may be allocated with and transmit the PUCCH only in the P cellthereof and use only the P cell to acquire the system information orchange a monitoring procedure. An evolved universal terrestrial radioaccess (E-UTRAN) may change only the P cell for the handover procedureto the terminal supporting the carrier aggregation environment by usingan RRC connection reconfiguration message (RRCConnectionReconfigutaion)message of an upper layer including mobile control information(mobilityControlInfo).

The S cell means a cell that operates on a secondary frequency(alternatively, secondary CC). Only one P cell may be allocated to aspecific terminal and one or more S cells may be allocated to thespecific terminal. The S cell may be configured after RRC connectionestablishment is achieved and used for providing an additional radioresource. The PUCCH is not present in residual cells other than the Pcell, that is, the S cells among the serving cells configured in thecarrier aggregation environment. The E-UTRAN may provide all systeminformation associated with a related cell which is in an RRC_CONNECTEDstate through a dedicated signal at the time of adding the S cells tothe terminal that supports the carrier aggregation environment. A changeof the system information may be controlled by releasing and adding therelated S cell and in this case, the RRC connection reconfiguration(RRCConnectionReconfigutaion) message of the upper layer may be used.The E-UTRAN may perform having different parameters for each terminalrather than broadcasting in the related S cell.

After an initial security activation process starts, the E-UTRAN addsthe S cells to the P cell initially configured during the connectionestablishment process to configure a network including one or more Scells. In the carrier aggregation environment, the P cell and the S cellmay operate as the respective component carriers. In an embodimentdescribed below, the primary component carrier (PCC) may be used as thesame meaning as the P cell and the secondary component carrier (SCC) maybe used as the same meaning as the S cell.

FIG. 7 illustrates examples of a component carrier and carrieraggregation in the wireless communication system to which the presentinvention can be applied.

FIG. 7a illustrates a single carrier structure used in an LTE system.The component carrier includes the DL CC and the UL CC. One componentcarrier may have a frequency range of 20 MHz.

FIG. 7b illustrates a carrier aggregation structure used in the LTEsystem. In the case of FIG. 7b , a case is illustrated, in which threecomponent carriers having a frequency magnitude of 20 MHz are combined.Each of three DL CCs and three UL CCs is provided, but the number of DLCCs and the number of UL CCs are not limited. In the case of carrieraggregation, the terminal may simultaneously monitor three CCs, andreceive downlink signal/data and transmit uplink signal/data.

When N DL CCs are managed in a specific cell, the network may allocate M(M≤N) DL CCs to the terminal. In this case, the terminal may monitoronly M limited DL CCs and receive the DL signal. Further, the networkgives L (L≤M≤N) DL CCs to allocate a primary DL CC to the terminal andin this case, UE needs to particularly monitor L DL CCs. Such a schememay be similarly applied even to uplink transmission.

A linkage between a carrier frequency (alternatively, DL CC) of thedownlink resource and a carrier frequency (alternatively, UL CC) of theuplink resource may be indicated by an upper-layer message such as theRRC message or the system information. For example, a combination of theDL resource and the UL resource may be configured by a linkage definedby system information block type 2 (SIB2). In detail, the linkage maymean a mapping relationship between the DL CC in which the PDCCHtransporting a UL grant and a UL CC using the UL grant and mean amapping relationship between the DL CC (alternatively, UL CC) in whichdata for the HARQ is transmitted and the UL CC (alternatively, DL CC) inwhich the HARQ ACK/NACK signal is transmitted.

If one or more S cells are configured in a UE, a network may activate ordeactivate the configured S cell(s). A P cell is always activated. Thenetwork activates or deactivates the S cell(s) by sending anactivation/deactivation MAC control element.

The activation/deactivation MAC control element has a fixed size andincludes a single octet including seven C fields and one R field. The Cfield is configured for each S cell index “SCellIndex”, and indicatesthe activation/deactivation state of the S cell. When the value of the Cfield is set to “1”, it indicates that an S cell having a correspondingS cell index is activated. When the value of the C field is set to “0”,it indicates that an S cell having a corresponding S cell index isdeactivated.

Furthermore, the UE maintains a timer “sCellDeactivationTimer” for eachconfigured S cell and deactivates a related S cell when the timerexpires. The same initial value of the timer is applied to each instanceof the timer “sCellDeactivationTimer” and set by RRC signaling. When theS cell(s) are added or after handover, initial S cell(s) are adeactivation state.

The UE performs the following operation on each of the configured Scell(s) in each TTI.

When the UE receives an activation/deactivation MAC control element thatactivates an S cell in a specific TTI (subframe n), the UE activates theS cell in a corresponding TTI (a subframe n+8 or thereafter) onpredetermined timing and (re)starts a timer related to the correspondingS cell. What the UE activates the S cell means that the UE applies acommon S cell operation, such as the transmission of a soundingreference signal (SRS), the reporting of a channel quality indicator(CQI)/precoding matrix indicator (PMI)/rank indication (RI)/precodingtype indicator (PTI), the monitoring of a PDCCH and the monitoring of aPDCCH for an S cell on the S cell.

When the UE receives an activation/deactivation MAC control element thatdeactivates an S cell in a specific TTI (subframe n) or a timer relatedto a specific TTI (subframe n)-activated S cell expires, the UEdeactivates the S cell in a corresponding TTI (subframe n+8 orthereafter) on predetermined timing, stops the timer of thecorresponding S cell, and flushes all of HARQ buffers related to thecorresponding S cell.

If a PDCCH on an activated S cell indicates an uplink grant or downlinkassignment or a PDCCH on a serving cell that schedules the activated Scell indicates an uplink grant or downlink assignment for the activatedS cell, the UE restarts a timer related to the corresponding S cell.

When the S cell is deactivated, the UE does not send an SRS on the Scell, does not report a CQI/PMI/RI/PTI for the S cell, does not send anUL-SCH on the S cell, and does not monitor a PDCCH on the S cell.

Random Access Procedure

A random access procedure provided by LTE/LTE-A systems is describedbelow.

The random access procedure is used for a UE to obtain uplinksynchronization with an eNB or to have uplink radio resources allocatedthereto. When the UE is powered on, the UE obtains downlinksynchronization with an initial cell and receives system information.The UE obtains information about a set of available random accesspreambles and radio resources used to send a random access preamble fromthe system information. The radio resources used to send the randomaccess preamble may be specified as a combination of at least onesubframe index and an index in a frequency domain. The UE sends a randomaccess preamble randomly selected from the set of random accesspreambles. An eNB that has received the random access preamble sends atiming alignment (TA) value for uplink synchronization to the UE througha random access response. Accordingly, the UE obtains uplinksynchronization.

The random access procedure is common to frequency division duplex (FDD)and time division duplex (TDD). The random access procedure is notrelated to a cell size and is also not related to the number of servingcells if a component aggregation (CA) has been configured.

First, the UE may perform the random access procedure as in thefollowing cases.

If the UE performs initial access in the RRC idle state because it doesnot have RRC connection with the eNB

If the UE performs an RRC connection re-establishment procedure

If the UE first accesses a target cell in a handover process

If the random access procedure is requested by a command from the eNB

If there is data to be transmitted in downlink in an uplinknon-synchronized situation during the RRC connection state

If there is a data to be transmitted in uplink in an uplinknon-synchronized situation or in a situation in which designated radioresources used to request radio resources have not been allocated duringthe RRC connection state

If the positioning of the UE is performed in a situation in which timingadvance is necessary during the RRC connection state

If a recovery process is performed when a radio link failure or handoverfailure occurs

In 3GPP Rel-10, a method for applying a timing advance (TA) valueapplicable to one specific cell (e.g., a P cell) to a plurality of cellsin common in a radio access system supporting a component aggregationhas been taken into consideration. A UE may aggregate a plurality ofcells belonging to different frequency bands (i.e., greatly spaced aparton the frequency) or a plurality of cells having different propagationproperties. Furthermore, in the case of a specific cell, in order toexpand coverage or remove a coverage hole, if the UE performscommunication with an eNB (i.e., a macro eNB) through one cell andperforms communication with a secondary eNB (SeNB) through the othercell in a situation in which a remote radio header (RRH) (i.e.,repeater), a small cell such as a femto cell or a pico cell, or the SeNBhas been disposed within the cell, a plurality of cells may havedifferent delay properties. In this case, if the UE performs uplinktransmission using a method for applying one TA value to a plurality ofcells in common, the synchronization of an uplink signal transmitted onthe plurality of cells may be severely influenced. Accordingly, aplurality of TAs may be used in a CA situation in which a plurality ofcells has been aggregated. In 3GPP Rel-11, in order to support multipleTAs, the independent allocation of the TAs may be taken intoconsideration for each specific cell group. This is called a TA group(TAG). The TAG may include one or more cells. The same TA may be appliedto one or more cells included in a TAG in common. In order to supportsuch multiple TAs, an MAC TA command control element includes a TAGidentity (ID) of 2 bits and a TA command field of 6 bits.

A UE in which a CA has been configured performs a random accessprocedure if it performs the random access procedure in relation to a Pcell. In the case of a TAG to which the P cell belongs (i.e., a primaryTAG (pTAG)), as in a conventional technology, TA determined based on theP cell or coordinated through a random access procedure involved in theP cell may be applied to all of cell(s) within the pTAG In contrast, inthe case of a TAG including only an S cell (i.e., a secondary TAG(sTAG)), TA determined based on a specific S cell within the sTAG may beapplied to all of cell(s) within the corresponding sTAG In this case,the TA may be obtained by a random access procedure initiated by an eNB.More specifically, the S cell is configured as a random access channel(RACH) resource within the sTAG In order to determine the TA, the eNBrequests RACH access in the S cell. That is, the eNB initiates RACHtransmission on S cells in response to a PDCCH order transmitted in theP cell. A response message for an S cell preamble is transmitted througha P cell using an RA-RNTI. The UE may apply TA, determined based on an Scell to which random access has been successfully completed, to all ofcell(s) within a corresponding sTAG As described above, the randomaccess procedure may be performed even in an S cell in order to obtainthe TA of an sTAG to which the S cell belongs even in the correspondingS cell.

An LTE/LTE-A system provides a contention-based random access procedurefor randomly selecting, by a UE, one preamble within a specific set andusing the selected preamble and a non-contention-based random accessprocedure for using a random access preamble allocated to only aspecific UE by an eNB in a process of selecting a random access preamble(RACH preamble). In this case, the non-contention-based random accessprocedure may be used for only UE positioning and/or timing advancealignment for an sTAG if it is requested in the handover process or inresponse to a command from the eNB. After the random access procedure iscompleted, common uplink/downlink transmission is performed.

A relay node (RN) also supports both the contention-based random accessprocedure and the non-contention-based random access procedure. When arelay node performs the random access procedure, it suspends an RNsubframe configuration at that point of time. That is, this means thatit temporarily discards an RN subframe. Thereafter, an RN subframeconfiguration is restarted at a point of time at which a random accessprocedure is successfully completed.

FIG. 8 is a diagram for illustrating a contention-based random accessprocedure in a wireless communication system to which an embodiment ofthe present invention may be applied.

(1) First Message (Msg 1 or Message 1)

First, UE randomly selects one random access preamble (RACH preamble)from a set of random access preambles indicated by system information ora handover command, selects a physical RACH (PRACH) resource capable ofsending the random access preamble, and sends the selected physical RACH(PRACH).

The random access preamble is transmitted through 6 bits in an RACHtransport channel. The 6 bits include a random identity of 5 bits foridentifying the UE that has performed RACH transmission and 1 bit (e.g.,indicate the size of a third message Msg3) for indicating additionalinformation.

An eNB that has received the random access preamble from the UE decodesthe random access preamble and obtains an RA-RNTI. The RA-RNTI relatedto the PRACH in which the random access preamble has been transmitted isdetermined by the time-frequency resource of the random access preambletransmitted by the corresponding UE.

(2) Second Message (Msg 2 or Message 2)

The eNB sends a random access response, addressed by the RA-RNTIobtained through the preamble on the first message, to the UE. Therandom access response may include a random access (RA) preambleindex/identifier, uplink (UL) assignment providing notification ofuplink radio resources, a temporary C-RNTI, and a time alignment command(TAC). The TAC is information indicative of a time alignment commandthat is transmitted from the eNB to the UE in order to maintain uplinktime alignment. The UE updates uplink transmission timing using the TAC.When the UE updates time synchronization, it initiates or restarts atime alignment timer. An UL grant includes uplink resource allocationused for the transmission of a scheduling message (third message) to bedescribed later and a transmit power command (TPC). The TPC is used todetermine transmission power for a scheduled PUSCH.

After the UE sends the random access preamble, it attempts to receiveits own random access response within a random access response windowindicated by the eNB through system information or a handover command,detects a PDCCH masked with an RA-RNTI corresponding to the PRACH, andreceives a PDSCH indicated by the detected PDCCH. Information about therandom access response may be transmitted in the form of a MAC packetdata unit (PDU). The MAC PDU may be transferred through the PDSCH. ThePDCCH may include information about the UE that needs to receive thePDSCH, information about the frequency and time of the radio resourcesof the PDSCH, and the transmission format of the PDSCH. As describedabove, once the UE successfully detects the PDCCH transmitted thereto,it may properly receive the random access response transmitted throughthe PDSCH based on the pieces of information of the PDCCH.

The random access response window means a maximum time interval duringwhich the UE that has sent the preamble waits to receive the randomaccess response message. The random access response window has a lengthof “ra-ResponseWindowSize” that starts from a subframe subsequent tothree subframes from the last subframe in which the preamble istransmitted. That is, the UE waits to receive the random access responseduring a random access window secured after three subframes from asubframe in which the preamble has been transmitted. The UE may obtainthe parameter value of a random access window size“ra-ResponseWindowsize” through the system information. The randomaccess window size may be determined to be a value between 2 and 10.

When the UE successfully receives the random access response having thesame random access preamble index/identifier as the random accesspreamble transmitted to the eNB, it suspends the monitoring of therandom access response. In contrast, if the UE has not received a randomaccess response message until the random access response window isterminated or the UE does not receive a valid random access responsehaving the same random access preamble index as the random accesspreamble transmitted to the eNB, the UE considers the reception of arandom access response to be a failure and then may perform preambleretransmission.

As described above, the reason why the random access preamble index isnecessary for the random access response is to provide notification thatan UL grant, a TC-RNTI and a TAC are valid for which UE because randomaccess response information for one or more UEs may be included in onerandom access response.

(3) Third Message (Msg 3 or Message 3)

When the UE receives a valid random access response, it processes eachof pieces of information included in the random access response. Thatis, the UE applies a TAC to each of the pieces of information and storesa TC-RNTI. Furthermore, the UE sends data, stored in the buffer of theUE, or newly generated data to the eNB using an UL grant. If the UEperforms first connection, an RRC connection request generated in theRRC layer and transferred through a CCCH may be included in the thirdmessage and transmitted. In the case of an RRC connectionre-establishment procedure, an RRC connection re-establishment requestgenerated in the RRC layer and transferred through a CCCH may beincluded in the third message and transmitted. Furthermore, the thirdmessage may include an NAS access request message.

The third message may include the identity of the UE. In thecontention-based random access procedure, the eNB is unable to determinewhich UE can perform the random access procedure. The reason for this isthat the UE has to be identified in order to perform a collisionresolution.

A method for including the identity of UE includes two methods. In thefirst method, if UE has already had a valid cell identity (C-RNTI)allocated in a corresponding cell prior to a random access procedure,the UE sends its own cell identity through an uplink transmission signalcorresponding to an UL grant. In contrast, if a valid cell identity hasnot been allocated to the UE prior to a random access procedure, the UEincludes its own unique identity (e.g., an S-TMSI or a random number) inan uplink transmission signal and sends the uplink transmission signal.In general, the unique identity is longer than a C-RNTI. In transmissionon an UL-SCH, UE-specific scrambling is used. In this case, if a C-RNTIhas not been allocated to the UE, the scrambling may not be based on theC-RNTI, and instead a TC-RNTI received in a random access response isused. If the UE has sent data corresponding to the UL grant, itinitiates a timer for a collision resolution (i.e., a contentionresolution timer).

(4) Fourth Message (Msg 4 or Message 4)

When the C-RNTI of the UE is received through the third message from theUE, the eNB sends a fourth message to the UE using the received C-RNTI.In contrast, when the eNB receives a unique identity (i.e., an S-TMSI ora random number) through the third message from the UE, it sends thefourth message to the UE using a TC-RNTI allocated to the correspondingUE in a random access response. In this case, the fourth message maycorrespond to an RRC connection setup message including a C-RNTI.

After the UE sends data including its own identity through the UL grantincluded in the random access response, it waits for an instruction fromthe eNB for a collision resolution. That is, the UE attempts to receivea PDCCH in order to receive a specific message. A method for receivingthe PDCCH includes two methods. As described above, if the third messagetransmitted in response to the UL grant includes a C-RNTI as its ownidentity, the UE attempts the reception of a PDCCH using its own C-RNTI.If the identity is a unique identity (i.e., an S-TMSI or a randomnumber), the UE attempts the reception of a PDCCH using a TC-RNTIincluded in the random access response. Thereafter, in the former case,if the UE has received a PDCCH through its own C-RNTI before a collisionresolution timer expires, the UE determines that the random accessprocedure has been normally performed and terminates the random accessprocedure. In the latter case, if the UE has received a PDCCH through aTC-RNTI before a collision resolution timer expires, the UE checks datain which a PDSCH indicated by the PDCCH is transferred. If, as a resultof the check, it is found that the unique identity of the UE has beenincluded in the contents of the data, the UE determines that the randomaccess procedure has been normally performed and terminates the randomaccess procedure. The UE obtains the C-RNTI through the fourth message.Thereafter, the UE and a network send or receive a UE-dedicated messageusing the C-RNTI.

A method for a collision resolution in random access is described below.

The reason why a collision occurs in performing random access is thatthe number of random access preambles is basically limited. That is, aUE randomly selects one of common random access preambles and sends theselected random access preamble because an eNB cannot assign a randomaccess preamble unique to a UE to all of UEs. Accordingly, two or moreUEs may select the same random access preamble and send it through thesame radio resources (PRACH resource), but the eNB determines thereceived random access preambles to be one random access preambletransmitted by one UE. For this reason, the eNB sends a random accessresponse to the UE, and expects that the random access response will bereceived by one UE. As described above, however, since a collision mayoccur, two or more UEs receive one random access response and thus theeNB performs an operation according to the reception of each randomaccess response for each UE. That is, there is a problem in that the twoor more UEs send different data through the same radio resources usingone UL grant included in the random access response. Accordingly, thetransmission of the data may all fail, and the eNB may receive only thedata of a specific UE depending on the location or transmission power ofthe UEs. In the latter case, all of the two or more UEs assume that thetransmission of their data was successful, and thus the eNB has tonotify UEs that have failed in the contention of information about thefailure. That is, providing notification of information about thefailure or success of the contention is called a collision resolution.

A collision resolution method includes two methods. One method is amethod using a collision resolution timer, and the other method is amethod of sending the identity of a UE that was successful in acontention to other UEs. The former method is used when a UE already hasa unique C-RNTI prior to a random access process. That is, the UE thathas already had the C-RNTI sends data, including its own C-RNTI, to aneNB in response to a random access response, and drives a collisionresolution timer. Furthermore, when PDCCH information indicated by itsown C-RNTI is received before the collision resolution timer expires,the UE determines that it was successful in the contention and normallyterminates the random access. In contrast, if the UE does not receive aPDCCH indicated by its own C-RNTI before the collision resolution timerexpires, the UE determines that it failed in the contention and mayperform a random access process again or may notify a higher layer ofthe failure of the contention. In the latter method of the twocontention resolution methods, that is, the method of sending theidentity of a successful UE, is used if a UE does not have a unique cellidentity prior to a random access process. That is, if the UE does nothave its own cell identity, the UE includes an identity (or an S-TMSI ora random number) higher than the cell identity in data based on UL grantinformation included in a random access response, sends the data, anddrives a collision resolution timer. If data including its own higheridentity is transmitted through a DL-SCH before the collision resolutiontimer expires, the UE determines that the random access process wassuccessful. In contrast, if data including its own higher identity isnot received through a DL-SCH before the collision resolution timerexpires, the UE determines that the random access process has failed.

Unlike in the contention-based random access procedure shown in FIG. 8,the operation in the non-contention-based random access procedure isterminated by only the transmission of the first message and the secondmessage. In this case, before a UE sends a random access preamble to aneNB as the first message, the eNB allocates the random access preambleto the UE, and the UE sends the allocated random access preamble to theeNB as the first message and receives a random access response from theeNB. Accordingly, the random connection procedure is terminated.

Reference Signal (RS)

In the wireless communication system, since the data is transmittedthrough the radio channel, the signal may be distorted duringtransmission. In order for the receiver side to accurately receive thedistorted signal, the distortion of the received signal needs to becorrected by using channel information. In order to detect the channelinformation, a signal transmitting method know by both the transmitterside and the receiver side and a method for detecting the channelinformation by using an distortion degree when the signal is transmittedthrough the channel are primarily used. The aforementioned signal isreferred to as a pilot signal or a reference signal (RS).

Recently, when packets are transmitted in most of mobile communicationsystems, multiple transmitting antennas and multiple receiving antennasare adopted to increase transceiving efficiency rather than a singletransmitting antenna and a single receiving antenna. When the data istransmitted and received by using the MIMO antenna, a channel statebetween the transmitting antenna and the receiving antenna need to bedetected in order to accurately receive the signal. Therefore, therespective transmitting antennas need to have individual referencesignals.

Reference signal in a wireless communication system can be mainlycategorized into two types. In particular, there are a reference signalfor the purpose of channel information acquisition and a referencesignal used for data demodulation. Since the object of the formerreference signal is to enable a UE (user equipment) to acquire a channelinformation in DL (downlink), the former reference signal should betransmitted on broadband. And, even if the UE does not receive DL datain a specific subframe, it should perform a channel measurement byreceiving the corresponding reference signal. Moreover, thecorresponding reference signal can be used for a measurement formobility management of a handover or the like. The latter referencesignal is the reference signal transmitted together when a base stationtransmits DL data. If a UE receives the corresponding reference signal,the UE can perform channel estimation, thereby demodulating data. And,the corresponding reference signal should be transmitted in a datatransmitted region.

The DL reference signals are categorized into a common reference signal(CRS) shared by all terminals for an acquisition of information on achannel state and a measurement associated with a handover or the likeand a dedicated reference signal (DRS) used for a data demodulation fora specific terminal. Information for demodulation and channelmeasurement may be provided by using the reference signals. That is, theDRS is used only for data demodulation only, while the CRS is used fortwo kinds of purposes including channel information acquisition and datademodulation.

The receiver side (that is, terminal) measures the channel state fromthe CRS and feeds back the indicators associated with the channelquality, such as the channel quality indicator (CQI), the precodingmatrix index (PMI), and/or the rank indicator (RI) to the transmittingside (that is, base station). The CRS is also referred to as acell-specific RS. On the contrary, a reference signal associated with afeed-back of channel state information (C SI) may be defined as CSI-RS.

The DRS may be transmitted through resource elements when datademodulation on the PDSCH is required. The terminal may receive whetherthe DRS is present through the upper layer and is valid only when thecorresponding PDSCH is mapped. The DRS may be referred to as theUE-specific RS or the demodulation RS (DMRS).

FIG. 9 illustrates a reference signal pattern mapped to a downlinkresource block pair in the wireless communication system to which thepresent invention can be applied.

Referring to FIG. 9, as a unit in which the reference signal is mapped,the downlink resource block pair may be expressed by one subframe in thetimedomain×12 subcarriers in the frequency domain. That is, one resourceblock pair has a length of 14 OFDM symbols in the case of a normalcyclic prefix (CP) (FIG. 9a ) and a length of 12 OFDM symbols in thecase of an extended cyclic prefix (CP) (FIG. 9b ). Resource elements(REs) represented as ‘0’, ‘1’, ‘2’, and ‘3’ in a resource block latticemean the positions of the CRSs of antenna port indexes ‘0’, ‘1’, ‘2’,and ‘3’, respectively and resource elements represented as ‘D’ means theposition of the DRS.

Hereinafter, when the CRS is described in more detail, the CRS is usedto estimate a channel of a physical antenna and distributed in a wholefrequency band as the reference signal which may be commonly received byall terminals positioned in the cell. That is, the CRS is transmitted ineach subframe across a broadband as a cell-specific signal. Further, theCRS may be used for the channel quality information (CSI) and datademodulation.

The CRS is defined as various formats according to an antenna array atthe transmitter side (base station). The RSs are transmitted based onmaximum 4 antenna ports depending on the number of transmitting antennasof a base station in the 3GPP LTE system (for example, release-8). Thetransmitter side has three types of antenna arrays of three singletransmitting antennas, two transmitting antennas, and four transmittingantennas. For instance, in case that the number of the transmittingantennas of the base station is 2, CRSs for antenna #1 and antenna #2are transmitted. For another instance, in case that the number of thetransmitting antennas of the base station is 4, CRSs for antennas #1 to#4 are transmitted.

When the base station uses the single transmitting antenna, a referencesignal for a single antenna port is arrayed.

When the base station uses two transmitting antennas, reference signalsfor two transmitting antenna ports are arrayed by using a time divisionmultiplexing (TDM) scheme and/or a frequency division multiplexing (FDM)scheme. That is, different time resources and/or different frequencyresources are allocated to the reference signals for two antenna portswhich are distinguished from each other.

Moreover, when the base station uses four transmitting antennas,reference signals for four transmitting antenna ports are arrayed byusing the TDM and/or FDM scheme. Channel information measured by adownlink signal receiving side (terminal) may be used to demodulate datatransmitted by using a transmission scheme such as single transmittingantenna transmission, transmission diversity, closed-loop spatialmultiplexing, open-loop spatial multiplexing, or multi-user MIMO.

In the case where the MIMO antenna is supported, when the referencesignal is transmitted from a specific antenna port, the reference signalis transmitted to the positions of specific resource elements accordingto a pattern of the reference signal and not transmitted to thepositions of the specific resource elements for another antenna port.That is, reference signals among different antennas are not duplicatedwith each other.

The DRS is described in more detail below. The DRS is used to demodulatedata. Precoding weight used for a specific UE in MIMO antennatransmission is used without any change in order for a UE to estimate acorresponding channel in association with a transport channeltransmitted in each transmission antenna when the UE receives areference signal.

The 3GPP LTE system (e.g., Release-8) supports up to a maximum of fourtransmission antennas, and a DRA for rank 1 beamforming is defined. TheDRS for rank 1 beamforming further indicates a reference signal anantenna port index 5.

The LTE-A system which is an evolved version of the LTE system shouldsupport maximum eight transmitting antennas for downlink transmission.Accordingly, reference signals for maximum eight transmitting antennasshould also be supported. In the LTE system, since the downlinkreference signals are defined for maximum four antenna ports, if thebase station includes four or more downlink transmitting antennas andmaximum eight downlink transmitting antennas in the LTE-A system, thereference signals for these antenna ports should be definedadditionally. The reference signals for maximum eight transmittingantenna ports should be designed for two types of reference signals,i.e., the reference signal for channel measurement and the referencesignal for data demodulation.

One of important considerations in designing the LTE-A system is thebackward compatibility. That is, the backward compatibility means thatthe LTE user equipment should be operated normally even in the LTE-Asystem without any problem and the LTE-A system should also support suchnormal operation. In view of reference signal transmission, thereference signals for maximum eight transmitting antenna ports should bedefined additionally in the time-frequency domain to which CRS definedin the LTE is transmitted on full band of each subframe. However, in theLTE-A system, if reference signal patterns for maximum eighttransmitting antennas are added to full band per subframe in the samemanner as the CRS of the existing LTE system, the RS overhead becomestoo great.

Accordingly, the reference signal designed newly in the LTE-A system maybe divided into two types. Examples of the two types of referencesignals include a channel state information-reference signal (CSI-RS)(or may be referred to as channel state indication-RS) for channelmeasurement for selection of modulation and coding scheme (MCS) and aprecoding matrix index (PMI), and a data demodulation-reference signal(DM-RS) for demodulation of data transmitted to eight transmittingantennas.

The CSI-RS for the channel measurement purpose is designed for channelmeasurement mainly unlike the existing CRS used for channel measurement,handover measurement, and data demodulation. The CSI-RS may also be usedfor handover measurement. Since the CSI-RS is transmitted only to obtainchannel state information, it may not be transmitted per subframe unlikethe CRS of the existing LTE system. Accordingly, in order to reduceoverhead, the CSI-RS may intermittently be transmitted on the time axis.

The DM-RS is dedicatedly transmitted to the UE which is scheduled in thecorresponding time-frequency domain for data demodulation. In otherwords, the DM-RS of a specific UE is only transmitted to the regionwhere the corresponding user equipment is scheduled, i.e., thetime-frequency domain that receives data.

In the LTE-A system, an eNB should transmit the CSI-RSs for all theantenna ports. Since the transmission of CSI-RSs for up to eighttransmission antenna ports in every subframe leads to too much overhead,the CSI-RSs should be transmitted intermittently along the time axis,thereby reducing CSI-RS overhead. Therefore, the CSI-RSs may betransmitted periodically at every integer multiple of one subframe, orin a predetermined transmission pattern. The CSI-RS transmission periodor pattern of the CSI-RSs may be configured by the eNB.

In order to measure the CSI-RSs, a UE should have knowledge of theinformation for each of the CSI-RS antenna ports in the cell to whichthe UE belong such as the transmission subframe index, thetime-frequency position of the CSI-RS resource element (RE) in thetransmission subframe, the CSI-RS sequence, and the like.

In the LTE-A system, an eNB should transmit each of the CSI-RSs formaximum eight antenna ports, respectively. The resources used fortransmitting the CSI-RS of different antenna ports should be orthogonal.When an eNB transmits the CSI-RS for different antenna ports, by mappingthe CSI-RS for each of the antenna ports to different REs, the resourcesmay be orthogonally allocated in the FDM/TDM scheme. Otherwise, theCSI-RSs for different antenna ports may be transmitted in the CDM schemewith being mapped to the mutually orthogonal codes.

When an eNB notifies the information of the CSI-RS to the UE in its owncell, the information of the time-frequency in which the CSI-RS for eachantenna port is mapped should be notified. Particularly, the informationincludes the subframe numbers on which the CSI-RS is transmitted, theperiod of the CSI-RS being transmitted, the subframe offset in which theCSI-RS is transmitted, the OFDM symbol number in which the CSI-RS RE ofa specific antenna is transmitted, the frequency spacing, the offset orshift value of RE on the frequency axis.

The CSI-RS is transmitted through 1, 2, 4 or 8 antenna ports. In thiscase, the antenna port which is used is p=15, p=15,16, p=15, . . . , 18,or p=15, . . . , 22. The CSI-RS may be defined only for the subcarrierinterval Δf=15 kHz

(k′, l′) (herein, k′ is a subcarrier index in a resource block, and l′represents an

OFDM symbol index in a slot) and the condition of n_(s) is determinedaccording to the CSI-RS configuration shown in Table 3 or Table 4 below.

Table 3 exemplifies the mapping of (k′, l′) according to the CSI-RSconfiguration for the normal CP.

TABLE 3 Number of CSI reference signals configured CSI reference signal1 or 2 4 8 configuration (k′, l′) n_(s) mod 2 (k′, l′) n_(s) mod 2 (k′,l′) n_(s) mod 2 Frame 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 1 (11, 2)  1 (11, 2) 1 (11, 2)  1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 3 (7, 2) 1 (7, 2) 1 (7, 2) 1 4(9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 0 6 (10, 2)  1 (10, 2)  1 7(8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1 (8, 5) 1 10 (3, 5) 0 11(2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15 (2, 2) 1 16 (1, 2) 1 17(0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame structure 20 (11, 1)  1 (11, 1) 1 (11, 1)  1 21 (9, 1) 1 (9, 1) 1 (9, 1) 1 22 (7, 1) 1 (7, 1) 1 (7, 1) 123 (10, 1)  1 (10, 1)  1 24 (8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26(5, 1) 1 27 (4, 1) 1 28 (3, 1) 1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

Table 4 exemplifies the mapping of (k′, l′) according to the CSI-RSconfiguration for the extended CP.

TABLE 4 Number of CSI reference signals configured CSI reference signal1 or 2 4 8 configuration (k′, l′) n_(s) mod 2 (k′, l′) n_(s) mod 2 (k′,l′) n_(s) mod 2 Frame structure 0 (11, 4)  0 (11, 4)  0 (11, 4)  0 type1 and 2 1 (9, 4) 0 (9, 4) 0 (9, 4) 0 2 (10, 4)  1 (10, 4)  1 (10, 4)  13 (9, 4) 1 (9, 4) 1 (9, 4) 1 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 0 6(4, 4) 1 (4, 4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4) 011 (0, 4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Framestructure 16 (11, 1)  1 (11, 1)  1 (11, 1)  1 type 2 only 17 (10, 1)  1(10, 1)  1 (10, 1)  1 18 (9, 1) 1 (9, 1) 1 (9, 1) 1 19 (5, 1) 1 (5, 1) 120 (4, 1) 1 (4, 1) 1 21 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1 24(6, 1) 1 25 (2, 1) 1 26 (1, 1) 1 27 (0, 1) 1

Referring to Table 3 and Table 4, for the CSI-RS transmission, in orderto decrease the inter-cell interference (ICI) in the multi-cellenvironment including the heterogeneous network (HetNet) environment,different configurations of maximum 32 (in the case of normal CP) ormaximum 28 (in the case of extended CP) are defined.

The CSI-RS configuration is different depending on the number of antennaports in a cell and the CP, neighbor cells may have differentconfigurations to the maximum. In addition, the CSI-RS configuration maybe divided into the case of being applied to both the FDD frame and theTDD frame and the case of being applied to only the TDD frame.

Based on Table 3 and Table 4, (k′, l′) and n_(s) are determinedaccording to the CSI-RS configuration. By applying these values toEquation 19, the time-frequency resource that each CSI-RS antenna portuses for transmitting the CSI-RS is determined.

FIG. 10 is a diagram illustrating the CSI-RS configuration in a wirelesscommunication system to which the present invention may be applied.

FIG. 10(a) shows twenty CSI-RS configurations that are usable in theCSI-RS transmission through one or two CSI-RS antenna ports, and FIG.10(b) shows ten CSI-RS configurations that are usable by four CSI-RSantenna ports. FIG. 10(c) shows five CSI-RS configurations that areusable in the CSI-RS transmission through eight CSI-RS antenna ports.

As such, according to each CSI-RS configuration, the radio resource(i.e., RE pair) in which the CSI-RS is transmitted is determined.

When one or two CSI-RS antenna ports are configured for transmitting theCSI-RS for a specific cell, the CSI-RS is transmitted on the radioresource according to the configured CSI-RS configuration among twentyCSI-RS configurations shown in FIG. 10(a).

Similarly, when four CSI-RS antenna ports are configured fortransmitting the CSI-RS for a specific cell, the CSI-RS is transmittedon the radio resource according to the configured CSI-RS configurationamong ten CSI-RS configurations shown in FIG. 10(b). In addition, wheneight CSI-RS antenna ports are configured for transmitting the CSI-RSfor a specific cell, the CSI-RS is transmitted on the radio resourceaccording to the configured CSI-RS configuration among five CSI-RSconfigurations shown in FIG. 10(c).

The CSI-RS for each of the antenna ports is transmitted with being CDMto the same radio resource for each of two antenna ports (i.e., {15,16},{17,18}, {19,20}, {21,22}). As an example of antenna ports 15 and 16,although the respective CSI-RS complex symbols are the same for antennaports 15 and 16, the CSI-RS complex symbols are mapped to the same radioresource with being multiplied by different orthogonal codes (e.g.,Walsh code). To the complex symbol of the CSI-RS for antenna port 15,[1, 1] is multiplied, and [1, −1] is multiplied to the complex symbol ofthe CSI-RS for antenna port 16, and the complex symbols are mapped tothe same radio resource. This procedure is the same for antenna ports{17,18}, {19,20} and {21,22}.

A UE may detect the CSI-RS for a specific antenna port by multiplying acode multiplied by the transmitted code. That is, in order to detect theCSI-RS for antenna port 15, the multiplied code [1 1] is multiplied, andin order to detect the CSI-RS for antenna port 16, the multiplied code[1-1] is multiplied.

Referring to FIGS. 10(a) to (c), when a radio resource is correspondingto the same CSI-RS configuration index, the radio resource according tothe CSI-RS configuration including a large number of antenna portsincludes the radio resource according to the CSI-RS configurationincluding a small number of antenna ports. For example, in the case ofCSI-RS configuration 0, the radio resource for eight antenna portsincludes all of the radio resource for four antenna ports and one or twoantenna ports.

A plurality of CSI-RS configurations may be used in a cell. Zero or oneCSI-RS configuration may be used for the non-zero power (NZP) CSI-RS,and zero or several CSI-RS configurations may be used for the zero powerCSI-RS.

A UE presumes the zero power transmission for the REs (except the caseof being overlapped with the RE that presumes the NZP CSI-RS that isconfigured by a high layer) that corresponds to four CSI-RS column inTable 3 and Table 4 above, for every bit that is configured as ‘1’ inthe Zero Power CSI-RS (ZP-CSI-RS) which is the bitmap of 16 bitsconfigured by a high layer. The Most Significant Bit (MSB) correspondsto the lowest CSI-RS configuration index, and the next bit in the bitmapcorresponds to the next CSI-RS configuration index in order.

The CSI-RS is transmitted in the downlink slot only that satisfies thecondition of n_(s) mod2 in Table 3 and Table 4 above and the CSI-RSsubframe configuration.

In the case of frame structure type 2 (TDD), in the subframe thatcollides with a special subframe, SS, PBCH or SIB 1(SystemInformationBlockTypel) message transmission or the subframe thatis configured to transmit a paging message, the CSI-RS is nottransmitted.

In addition, the RE in which the CSI-RS for a certain antenna port thatis belonged to an antenna port set S(S={15}, S={15,16}, S={17,18},S={19,20} or {S=21,22}) is transmitted is not used for transmitting thePDSCH or the CSI-RS of another antenna port.

Since the time-frequency resources used for transmitting the CSI-RS isunable to be used for transmitting data, the data throughput decreasesas the CSI-RS overhead increases. Considering this, the CSI-RS is notconfigured to be transmitted in every subframe, but configured to betransmitted in a certain transmission period that corresponds to aplurality of subframes. In this case, the CSI-RS transmission overheadmay be significantly decreased in comparison with the case that theCSI-RS is transmitted in every subframe.

The subframe period (hereinafter, referred to as ‘CSI-RS transmissionperiod’; T_(CSI-RS)) for transmitting the CSI-RS and the subframe offset(Δ_(CSI-RS)) are represented in Table 5 below.

Table 5 exemplifies the configuration of CSI-RS subframe.

TABLE 5 CSI-RS periodicity CSI-RS subframe offset CSI-RS-SubframeConfigT_(CSI-RS) Δ_(CSI-RS) I_(CSI-RS) (subframes) (subframes) 0-4 5I_(CSI-RS)  5-14 10 I_(CSI-RS) − 5  15-34 20 I_(CSI-RS) − 15 35-74 40I_(CSI-RS) − 35  75-154 80 I_(CSI-RS) − 75

Referring to Table 5, according to the CSI-RS subframe configuration(I_(CSI-RS)), the CSI-RS transmission period (T_(CSI-RS)) and thesubframe offset (Δ_(CSI-RS)) are determined.

The CSI-RS subframe configuration in Table 5 is configured as one of the‘SubframeConfig’ field and the ‘zeroTxPowerSubframeConfig’ field inTable 2 above. The CSI-RS subframe configuration may be separatelyconfigured for the NZP CSI-RS and the ZP CSI-RS.

The subframe including the CSI-RS satisfies Equation 12 below.(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  [Equation 12]

In Equation 12, T_(CSI-RS) represents the CSI-RS transmission period,Δ_(CSI-RS) represents the subframe offset value, n_(f) represents thesystem frame number, and n_(s) represents the slot number.

In the case of a UE in which transmission mode 9 is set for a servingcell, a single CSI-RS resource may be configured in the UE. In the caseof a UE in which transmission mode 10 is set for a serving cell, one ormore CSI-RS resources may be configured in the UE.

For each CSI-RS resource configuration, the following parameters may beset through high layer signaling.

If transmission mode 10 is set, the CSI-RS resource configurationidentifier

The number of CSI-RS ports

The CSI-RS configuration (refer to Table 3 and Table 4)

The CSI-RS subframe configuration (I_(CSI-RS); refer to Table 5)

If transmission mode 9 is set, the transmission power (P_(c)) for theCSI feedback

If transmission mode 10 is set, the transmission power (P_(c)) for theCSI feedback with respect to each CSI process. When the CSI subframesets C_(CSI,0) and C_(CSI,1) are set by a high layer for the CSIprocess, P_(c) is set in each CSI subframe set of the CSI process.

The pseudo-random sequence generator parameter (n_(ID))

If transmission mode 10 is set, the QCL scrambling identifier(qcl-ScramblingIdentity-r11) for assuming the Quasi Co-Located (QCL)type B UE, the CRS port count (crs-PortsCount-r11), and the high layerparameter (‘qcl-CRS-Info-r11’) that includes the MBSFN subframeconfiguration list (mbsfn-SubframeConfigList-r11) parameter.

When the CSI feedback value obtained by a UE has the value in the rangeof [−8, 15] dB, P_(c) is presumed by the ratio of the PDSCH EPRE for theCSI-RS EPRE. Herein, the PDSCH EPRE corresponds to the symbol in whichthe ratio of PDSCH EPRE for the CRS EPRE is ρ_(A).

In the same subframe of a serving cell, the CSI-RS and the PMCH are notconfigured together.

When four CRS antenna ports are configured in frame structure type 2,the CSI-RS configuration index belonged to [20-31] set in the case ofthe normal CP (refer to Table 3) or [16-27] set in the case of theextended CP (refer to Table 4) is not configured to a UE.

A UE may assume that the CSI-RS antenna port of the CSI-RS resourceconfiguration has the QCL relation with the delay spread, the Dopplerspread, the Doppler shift, the average gain and the average delay.

The UE to which transmission mode 10 and QCL type B are configured mayassume that the antenna ports 0 to 3 corresponding to the CSI-RSresource configuration and the antenna ports 15 to 22 corresponding tothe CSI-RS resource configuration have the QCL relation with the Dopplerspread and the Doppler shift.

For the UE to which transmission mode 10 is configured, one or moreChannel-State Information-Interference Measurement (CSI-IM) resourceconfiguration may be set.

The following parameters may be configured for each CSI-IM resourceconfiguration through high layer signaling.

The ZP CSI-RS configuration (refer to Table 3 and Table 4)

The ZP CSI-RS subframe configuration (I_(CSI-RS); refer to Table 5)

The CSI-IM resource configuration is the same as one of the configuredZP CSI-RS resource configuration.

In the same subframe in a serving cell, the CSI-IM resource and the PMCHare not configured simultaneously.

For a UE in which transmission modes 1 to 9 are set, a ZP CSI-RSresource configuration may be configured in the UE for a serving cell.For a UE in which transmission mode 10 is set, one or more ZP CSI-RSresource configurations may be configured in the UE for the servingcell.

The following parameters may be configured for the ZP CSI-RS resourceconfiguration through high layer signaling.

The ZP CSI-RS configuration list (refer to Table 3 and Table 4)

The ZP CSI-RS subframe configuration (I_(CSI-RS); refer to Table 5)

In the same subframe in a serving cell, the ZP CSI-RS resource and thePMCH are not configured simultaneously.

Cell Measurement/Measurement Report

For one or several methods among the several methods (handover, randomaccess, cell search, etc.) for guaranteeing the mobility of UE, the UEreports the result of a cell measurement to an eNB (or network).

In the 3GPP LTE/LTE-A system, the cell-specific reference signal (CRS)is transmitted through 0, 4, 7 and 11^(th) OFDM symbols in each subframeon the time axis, and used for the cell measurement basically. That is,a UE performs the cell measurement using the CRS that is received from aserving cell and a neighbor cell, respectively.

The cell measurement is the concept that includes the Radio resourcemanagement (RRM) measurement such as the Reference signal receive power(RSRP) that measures the signal strength of the serving cell and theneighbor cell or the signal strength in comparison with total receptionpower, and so on, the Received signal strength indicator (RSSI), theReference signal received quality (RSRQ), and the like and the RadioLink Monitoring (RLM) measurement that may evaluate the radio linkfailure by measuring the link quality from the serving cell.

The RSRP is a linear average of the power distribution of the RE inwhich the CRS is transmitted in a measurement frequency band. In orderto determine the RSRP, CRS (R0) that corresponds to antenna port ‘0’ maybe used. In addition, in order to determine the RSRP, CRS (R1) thatcorresponds to antenna port ‘1’ may be additionally used. The number ofREs used in the measurement frequency band and the measurement durationby a UE in order to determine the RSRP may be determined by the UEwithin the limit that satisfies the corresponding measurement accuracyrequirements. In addition, the power per RE may be determined by theenergy received in the remaining part of the symbol except the CP.

The RSSI is obtained as the linear average of the total reception powerthat is detected from all sources including the serving cell and thenon-serving cell of the co-channel, the interference from an adjacentchannel, the thermal noise, and so on by the corresponding UE in theOFDM symbols including the RS that corresponds to antenna port ‘0’. Whena specific subframe is indicated by high layer signaling for performingthe RSRQ measurement, the RSSI is measured through all OFDM symbols inthe indicated subframes.

The RSRQ is obtained by N×RSRP/RSSI. Herein, N means the number of RBsof the RSSI measurement bandwidth. In addition, the measurement of thenumerator and the denominator in the above numerical expression may beobtained by the same RB set.

A BS may forward the configuration information for the measurement to aUE through high layer signaling (e.g., RRC Connection Reconfigurationmessage).

The RRC Connection Reconfiguration message includes a radio resourceconfiguration dedicated (‘radioResourceConfigDedicated’) InformationElement (IE) and the measurement configuration (‘measConfig’) IE.

The ‘measConfig’ IE specifies the measurement that should be performedby the UE, and includes the configuration information for theintra-frequency mobility, the inter-frequency mobility, the inter-RATmobility as well as the configuration of the measurement gap.

Particularly, the ‘measConfig’ IE includes ‘measObjectToRemoveList’ thatrepresents the list of the measurement object (‘measObject’) that is tobe removed from the measurement and ‘measObjectToAddModList’ thatrepresents the list that is going to be newly added or amended. Inaddition, ‘MeasObjectCDMA2000’, ‘MeasObjctEUTRA’, ‘MeasObjectGERAN’ andso on are included in the ‘measObject’ according to the communicationtechnique.

The ‘RadioResourceConfigDedicated’ IE is used to setup/modify/releasethe Radio Bearer, to change the MAC main configuration, to change theSemi-Persistent Scheduling (SPS) configuration and to change thededicated physical configuration.

The ‘RadioResourceConfigDedicated’ IE includes the‘measSubframePattern-Serv’ field that indicates the time domainmeasurement resource restriction pattern for serving cell measurement.In addition, the ‘RadioResourceConfigDedicated’ IE includes‘measSubframeCellList’ indicating the neighbor cell that is going to bemeasured by the UE and ‘measSubframePattern-Neigh’ indicating the timedomain measurement resource restriction pattern for neighbor cellmeasurement.

The time domain measurement resource restriction pattern that isconfigured for the measuring cell (including the serving cell and theneighbor cell) may indicate at least one subframe per radio frame forperforming the RSRQ measurement. The RSRQ measurement is performed onlyfor the subframe indicated by the time domain measurement resourcerestriction pattern that is configured for the measuring cell.

As such, a UE (e.g., 3GPP Rel-10) should measure the RSRQ only in theduration configured by the subframe pattern (‘measSubframePattern-Serv’)for the serving cell measurement and the subframe pattern(‘measSubframePattern-Neigh’) for the neighbor cell measurement.

Although the measurement in the pattern for the RSRQ is not limited, butit is preferable to be measured only in the pattern for the accuracyrequirement.

Quasi Co-Located (QCL) Between Antenna Ports

Quasi co-located and quasi co-location (QC/QCL) may be defined asfollows.

If two antenna ports have a QC/QCL relation (or subjected to QC/QCL), aUE may assume that the large-scale property of a signal transferredthrough one antenna port may be inferred from a signal transferredthrough the other antenna port. In this case, the large-scale propertyincludes one or more of delay spread, Doppler spread, a frequency shift,average received power, and reception timing.

Furthermore, the following may be defined. Assuming that two antennaports have a QC/QCL relation (or subjected to QC/QCL), a UE may assumethat the large-scale property of a channel transferred through oneantenna port may be inferred from a wireless channel transferred throughthe other antenna port. In this case, the large-scale property includesone or more of delay spread, Doppler spread, Doppler shift, an averagegain, and average delay.

That is, if two antenna ports have a QC/QCL relation (or subjected toQC/QCL), it means that the large-scale property of a wireless channelfrom one antenna port is the same as the large-scale property of awireless channel from the other antenna port. Assuming that a pluralityof antenna ports in which an RS is transmitted is taken intoconsideration, if antenna ports on which two types of different RSs aretransmitted have a QCL relation, the large-scale property of a wirelesschannel from one antenna port may be replaced with the large-scaleproperty of a wireless channel from the other antenna port.

In this specification, the QC/QCL-related definitions are notdistinguished. That is, the QC/QCL concept may comply with one of thedefinitions. In a similar other form, the QC/QCL concept definition maybe changed in a form in which antenna ports having an established QC/QCLassumption may be assumed to be transmitted at the same location (i.e.,co-location) (e.g., a UE may assume antenna ports to be antenna portstransmitted at the same transmission point). The spirit of the presentinvention includes such similar modifications. In an embodiment of thepresent invention, the QC/QCL-related definitions are interchangeablyused, for convenience of description.

In accordance with the concept of the QC/QCL, a UE may not assume thesame large-scale property between wireless channels from correspondingantenna ports with respect to non-QC/QCL antenna ports. That is, in thiscase, a UE may perform independent processing on timing acquisition andtracking, frequency offset estimation and compensation, delayestimation, and Doppler estimation for each configured non-QC/QCLantenna port.

There are advantages in that a UE can perform the following operationsbetween antenna ports capable of an assuming QC/QCL:

With respect to delay spread and Doppler spread, a UE may identicallyapply the results of a power-delay profile, delay spread and a Dopplerspectrum, and Doppler spread estimation for a wireless channel from anyone antenna port to a Wiener filter which is used upon channelestimation for a wireless channel from other antenna ports.

With respect to a frequency shift and received timing, a UE may performtime and frequency synchronization on any one antenna port and thenapply the same synchronization to the demodulation of other antennaports.

With respect to average received power, a UE may average referencesignal received power (RSRP) measurement for two or more antenna ports.

For example, if a DMRS antenna port for downlink data channeldemodulation has been subjected to QC/QCL with the CRS antenna port of aserving cell, a UE may apply the large-scale property of a wirelesschannel, estimated from its own CRS antenna port upon channel estimationthrough the corresponding DMRS antenna port, in the same manner, therebyimproving reception performance of a DMRS-based downlink data channel.

The reason for this is that an estimation value regarding a large-scaleproperty can be more stably obtained from a CRS because the CRS is areference signal that is broadcasted with relatively high density everysubframe and in a full bandwidth. In contrast, a DMRS is transmitted ina UE-specific manner with respect to a specific scheduled RB, and theprecoding matrix of a precoding resource block group (PRG) unit that isused by an eNB for transmission may be changed. Thus, a valid channelreceived by a UE may be changed in a PRG unit. Accordingly, although aplurality of PRGs has been scheduled in the UE, performancedeterioration may occur when the DMRS is used to estimate thelarge-scale property of a wireless channel over a wide band.Furthermore, a CSI-RS may also have a transmission cycle ofseveral˜several tens of ms, and each resource block has also low densityof 1 resource element for each antenna port in average. Accordingly, theCSI-RS may experience performance deterioration if it is used toestimate the large-scale property of a wireless channel.

That is, a UE can perform the detection/reception, channel estimation,and channel state report of a downlink reference signal through a QC/QCLassumption between antenna ports.

Restricted RLM and RRM/CSI Measurement

As one of methods for interference coordination, an aggressor cell mayuse a silent subframe (or may be called an almost blank subframe (ABS))in which the transmission power/activity of partial physical channelsare reduced (in this case, to reduce the transmission power/activity mayinclude an operation for configuring the transmission power/activity tozero power). A victim cell may perform time domain inter-cellinterference coordination for scheduling UE by taking into considerationthe silent subframe.

In this case, from a standpoint of a victim cell UE, an interferencelevel may greatly vary depending on a subframe.

In such a situation, in order to perform a radio resource management(RRM) operation for measuring more accurate radio link monitoring (RLM)or RSRP/RSRQ in each subframe or to measure channel state information(CSI) for link adaptation, the monitoring/measurement may be restrictedto sets of subframes having a uniform interference characteristic. Inthe 3GPP LTE system, restricted RLM and RRM/CSI measurement are definedas follows.

A UE monitors downlink link quality based on a cell-specific referencesignal (CRS) in order to sense downlink link quality of a PCell. The UEestimates downlink radio link quality, and compares the estimate of athreshold Q_out with the estimate of a threshold Q_in order to monitorthe downlink radio link quality of the PCell.

The threshold Q_out is defined as a level at which downlink radio linkcannot be reliably received, and corresponds to a 10% block error rate(BER) of hypothetical PDCCH transmission in which a PCFICH error hasbeen taken into consideration based on transmission parameters listed inTable 6 below.

The threshold Q_in is defined as a level at which downlink radio linkquality can be more significantly reliably received compared to downlinkradio link quality in the threshold Q_out, and corresponds to a 2% BERof hypothetical PDCCH transmission in which a PCFICH error has beentaken into consideration based on transmission parameters listed inTable 7 below.

When higher layer signaling indicates a specific subframe for restrictedRLM, radio link quality is monitored.

Specific requirements are applied when a time domain measurementresource restriction pattern for performing RLM measurement isconfigured by a higher layer and if a time domain measurement resourcerestriction pattern configured for a cell to be measured indicates atleast one subframe per radio frame for performing RLM measurement.

If CRS assistance information is provided, the requirements may besatisfied when the number of transmit antennas of one or more cells towhich CRS assistance information has been provided is different from thenumber of transmit antennas of a cell in which RLM is performed.

If UE is not provided with CRS assistance information or CRS assistancedata is not valid for the entire evaluation period, a time domainmeasurement restriction may be applied when a collision occurs between aCRS and an ABS configured within a non-multicast broadcast singlefrequency network (MBSFN) subframe.

Table 6 illustrates PDCCH/PCFICH transmission parameters in anout-of-sync status.

TABLE 6 Attribute value DCI format 1A Number of control OFDM 2;bandwidth ≥ 10 MHz symbols 3; 3 MHz ≤ bandwidth ≤ 10 MHz 4; bandwidth =1.4 MHz Aggregation level (CCE) 4; bandwidth = 1.4 MHz 8; bandwidth ≥ 3MHz Ratio of PDCCH RE energy to 4 dB; if a single antenna port is usedaverage RS RE energy for CRS transmission by a PCell 1 dB; if two orfour antenna ports are used for CRS transmission by a PCell Ratio ofPCFICH RE energy to 4 dB; if a single antenna port is used average RS REenergy for CRS transmission by a PCell 1 dB: if two or four antennaports are used for CRS transmission by a PCell

Table 7 illustrates PDCCH/PCFICH transmission parameters in an in-syncstatus.

TABLE 7 Attribute Value DCI format 1C Number of control OFDM 2;bandwidth ≥ 10 MHz symbols 3; 3 MHz ≤ bandwidth ≤ 10 MHz 4; bandwidth =1.4 MHz Aggregation level (CCE) 4 Ratio of PDCCH RE 0 dB; If a singleantenna port is used energy to average for CRS transmission by a PCellRS RE energy −3 dB; If two or four antenna ports are used for CRStransmission by a PCell Ratio of PCFICH RE 4 dB; If a single antennaport is used energy to average for CRS transmission by a PCell RS REenergy 1 dB; If two or four antenna ports are used for CRS transmissionby a PCell

Downlink radio link quality for a PCell is monitored by a UE in order toindicate the out-of-sync status/in-sync status in a higher layer.

In a non-DRX mode operation, a physical layer of a UE assesses radiolink quality evaluated for a previous time interval by taking intoconsideration thresholds Q_out and Q_in in each radio frame.

If higher layer signaling indicates a specific subframe for restrictedRLM, the measurement of radio link quality is not performed in othersubframes not indicated in the higher layer signaling.

If radio link quality is poorer than the threshold Q_out, the physicallayer of a UE indicates the out-of-sync status for a higher layer withina radio frame whose radio link quality was measured. If the radio linkquality is better than the threshold Q_in, the physical layer of the UEindicates the in-sync status for the higher layer within a radio framewhose radio link quality was measured.

Massive MIMO

In a wireless communication system after LTE Release (Rel)-12, theintroduction of an active antenna system (AAS) is taken intoconsideration.

Unlike in an existing passive antenna system in which an amplifier andan antenna in which the phase and size of a signal can be adjusted havebeen separated, the AAS means a system in which each antenna isconfigured to include an active element, such as an amplifier.

The AAS does not require a separate cable, a connector, and otherhardware for connecting an amplifier and an antenna depending on use ofan active antenna and thus has high efficiency in terms of energy and anoperation cost. In particular, the AAS enables an advanced MIMOtechnology, such as the forming of an accurate beam pattern or 3-D beampattern in which a beam direction and a beam width have been taken intoconsideration, because the AAS supports an electronic beam controlmethod for each antenna.

Due to the introduction of an advanced antenna system, such as the AAS,a massive MIMO structure including a plurality of input/output antennasand a multi-dimensional antenna structure is also taken intoconsideration. For example, unlike in an existing straight-line antennaarray, if a 2-D antenna array is formed, a 3-D beam pattern may beformed by the active antenna of the AAS. If a 3-D beam pattern is usedfrom a viewpoint of a transmission antenna, the forming of a semi-staticor dynamic beam in the vertical direction of a beam in addition to thehorizontal direction can be performed. For example, an application, suchas the forming of a sector in the vertical direction may be taken intoconsideration.

Furthermore, from a viewpoint of a reception antenna, when a receptionbeam is formed using a massive reception antenna, an effect of a rise ofsignal power according to an antenna array gain may be expected.Accordingly, in the case of uplink, an eNB may receive a signaltransmitted by a UE through a plurality of antennas. In this case, thereis an advantage in that the UE can configure its own transmission powervery low by taking into consideration the gain of a massive receptionantenna in order to reduce an interference influence.

FIG. 11 illustrates a system having a plurality oftransmission/reception antennas through which an eNB or a UE is capableof three-dimensional (3-D) beamforming based on an AAS in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 11 is a diagram of the aforementioned example and illustrates a 3DMIMO system using a 2-D antenna array (i.e., a 2D-AAS).

Cell Coverage of Massive MIMO

A multiple antenna system, for example, a system having N transmissionantennas may perform beamforming so that received power is increased bya maximum of N times at a specific point, assuming that totaltransmission power is identically transmitted compared to a singleantenna system.

Even an eNB having multiple antennas, a channel that transfers a CRS, aPSS/SSS, a PBCH and broadcast information does not perform beamformingin a specific direction so that all of UEs within an eNB coverage areacan receive them.

In some cases, a PDSCH, that is, a channel that transfers unicastinformation to a specific UE, performs beamforming according to thelocation of a corresponding UE and link situation in order to improvetransmission efficiency. That is, the transmission data stream of thePDSCH is precoded in order to form a beam in a specific direction andtransmitted through multiple antenna ports. Accordingly, for example, iftransmission power of a CRS and transmission power of a PDSCH are thesame, received power of a precoded PDSCH beamformed toward acorresponding UE may be increased up to a maximum of N times compared toaverage received power of a CRS to a specific UE.

Up to now, in the LTE Rel-11 system, an eNB having a maximum of 8transmission antennas is taken into consideration. This means thatreceived power of a precoded PDSCH may be eight times greater thanaverage received power of a CRS. In the future, however, if the numberof transmission antennas of an eNB is 100 or more due to theintroduction of a massive MIMO system, a difference between receivedpower of a CRS and received power of a precoded PDSCH may be 100 timesor more. In conclusion, due to the introduction of the massive MIMOsystem, the coverage area of a CRS transmitted by a specific eNB and thecoverage area of a DM-RS-based PDSCH are not identical.

In particular, such a phenomenon may be significant if a difference inthe number of transmission antennas between two adjacent eNBs is great.A representative example includes an example in which a macro cellhaving 64 transmission antennas and a micro cell (e.g., a pico cell)having a single transmission antenna neighbor each other. A UE served inan initial deployment process of massive MIMO first expects that thenumber of antennas may be increased from many macro cells. Accordingly,in the case of a heterogeneous network in which a macro cell, a microcell and a pico cell are mixed, there is a great difference in thenumber of transmission antennas between adjacent eNBs.

For example, in the case of a pico cell having a single transmissionantenna, the coverage area of a CRS and the coverage area of a PDSCH arethe same. In the case of a macro cell having 64 transmission antennas,the coverage area of a PDSCH is greater than the coverage area of a CRS.Accordingly, if initial access and handover are determined based on onlyRSRP or RSRQ, that is, reception quality of the CRS, at the boundary ofthe macro cell and a pico cell, an eNB capable of providing the bestquality of the PDSCH may not be selected as a serving cell. As a simplesolution for this problem, PDSCH received power of an eNB having Ntransmission antennas may be assumed to be N times great, but such amethod is not the best solution if a case where the eNB cannot performbeamforming in all of directions as possible is taken intoconsideration.

RRM-RS

This specification proposes a method for sending a precoded referencesignal (RS) and performing RRM measurement on the precoded RS. In thisspecification, a precoded RS for this purpose is hereinafter referred toas an “RRM-RS.” The RRM-RS includes a plurality of antenna ports, andbeamforming is differently configured for each antenna port so that a UEcan measure RSRP for each transmission beam. For example, if an eNB isable to perform beamforming in M directions, an RRM-RS including M portsmay be configured.

Cycling and Multiplexing of RRM-RS

An M-port RRM-RS may be subjected to CDM or classified into FDM/TDM inthe same subframe and transmitted. That is, a transmission signal foreach antenna port of the M-port RRM-RS may be transmitted using adifferent transmission RE in the same subframe. If a transmission signalfor each antenna port of the M-port RRM-RS is transmitted using the sameRE, orthogonal scrambling code may be used between antenna ports inorder to avoid interference between the antenna ports.

In some cases, the number of antenna ports of an RRM-RS which may betransmitted in one subframe at the same time may be set as K, may bedivided into (M/K) subframes, and may be then transmitted.

In this case, the configuration parameter of the RRM-RS includes a totalnumber of antenna ports M and the number of antenna ports K transmittedin one subframe at the same time. The configuration parameter of theRRM-RS also includes an RRM-RS transmission cycle P and an offset O. Inthis case, the RRM-RS transmission cycle is defined as the interval ofsubframes in which an RRM-RS is transmitted. For example, if P=10, O=5,M=64, and K=32, the RRM-RS is transmitted in subframes having subframeindices (SFI) of 5, 15, 25, 35, . . . . In the subframe having SFI=5,No. 31 RRM-RS is transmitted in an antenna port 0. In the subframehaving SFI=15, No. 63 RRM-RS is transmitted in an antenna port 32. Inthe subframe having SFI=25, No. 31 RRM-RS is transmitted again in theantenna port 0.

In some cases, in a method for defining an RRM-RS transmission cycle asthe interval of subframes in which the RS of the same antenna port istransmitted, dividing the antenna ports of an RRM-RS into (M/K)subframes, and sending the antenna ports, the antenna ports are dividedinto (M/K) contiguous subframes and transmitted. For example, if P=20,O=5, M=64, and K=32, an RRM-RS is transmitted in subframes having SFIsof 5, 6, 25, 26, 45, 46, . . . . In the subframe having SFI=5, No. 31RRM-RS is transmitted in an antenna port 0. In the subframe havingSFI=6, No. 63 RRM-RS is transmitted in the antenna port 32. In thesubframe having SFI=25, No. 31 RRM-RS is transmitted again in theantenna port 0.

RSRP Measurement and Report

RSRP of an RRM-RS is measured and reported for each antenna port. Aplurality of RRM-RSs may be configured in a UE.

If each RRM-RS is transmitted by each cell, the configuration of RRM-RSstransmitted by a serving cell and neighboring cells may be designed to aUE. One cell may send a plurality of RRM-RSs. When a UE reports RSRP ofan RRM-RS, it also provides notification that the corresponding RSRPcorresponds to RSRP measurement results of which antenna port of whichRRM-RS.

In order to calculate RSRP of an RRM-RS, reception signal levels ofrespective antenna ports are averaged. A time window in which theaverage is calculated may be designed by an eNB, or RSRP may becalculated by averaging reception signal levels of the antenna ports ofRRM-RSs during a predetermined time (e.g., 200 ms). Alternatively, RSRPmay be calculated by filtering average received power obtained in eachtime window again.

A UE in which a plurality of RRM-RSs has been configured measures RSRPof each antenna port of each of the RRM-RSs. If R RRM-RSs have beenconfigured in a UE and the number of antenna ports of an r-th RRM-RS isM_r, RSRP of the m-th antenna port of the r-th RRM-RS is defined asRSRP(r,m). The UE aligns the RSRP(r,m), selects RSRP of L antenna portsthat belong to the aligned RSRP(r,m) and that are strongly received, andreports the selected RSRP.

As a slight modification method of the aforementioned method, a UEaligns RSRP(r,m), selects RSRP of antenna ports that belong to thealigned RSRP(r,m) and that are strongly received, and reports onlypieces of RSRP of ports that fall within a specific difference comparedto the RSRP of the selected antenna ports, that is, max(RSRP(r,m)). Thatis, RSRP of a maximum of L antenna ports, which has an RSRP differencegreater than a specific threshold in an RSRP ratio or dB scaleexpression as follows, is reported.RSRP(r,m)−max(RSRP(r,m))>Threshold  [Equation 13]

For another example, the antenna ports of a precoded CSI-RS configuredin a corresponding UE and an RRM-RS transmitted by a serving cell havinga similar beam direction may be designated as reference antenna ports.If the (m_0)-th antenna port of an (r_0)-th RRM-RS has been designed toa UE as a reference antenna port, the UE reports another antenna port ifa difference between RSRP of another antenna port and RSRP of thereference antenna port falls within a specific difference. That is, theUE reports an antenna port if a difference between pieces of RSRPexceeds a specific threshold in an RSRP ratio or dB scale expression asfollows.RSRP(r,m)−RSRP(r_0,m_0)>Threshold  [Equation 14]

FIG. 12 illustrates RSRP for each antenna port of an RRM-RS according toan embodiment of the present invention.

FIG. 12 shows an example of RSRP of each antenna port of an RRM-RSincluding 32 antenna ports.

If a UE has been configured to report RSRP of an antenna port havingRSRP of 5 dB or less compared to an antenna port having the greatestRSRP, the UE reports an antenna port having RSRP of more than 35 dBbecause an antenna port 13 has the greatest RSRP of 40 dB as in FIG. 12.That is, RSRP of antenna ports 24, 25 and 26 including the RSRP of theantenna port 13 is reported to an eNB.

Antenna Port Grouping

Beamforming may be differently configured for each antenna port. In thiscase, each antenna port corresponds to each beam.

Accordingly, each antenna port index (i) may be mapped to each beamindex (i). If beams are indexed so that the directions of an (i)-th beamand an (i+1)-th beam are adjacent, as in the example of FIG. 12, RSRPbetween adjacent antenna ports has a similar characteristic. Suchsimilarity is also generated between the (i)-th beam and an (i+c)-thbeam, but is reduced as “c” increases. Whether high similarity isgenerated between some continuous and adjacent beams is determined bythe interval of beams, the width of a beam, and the scattering degree ofmulti-paths.

An eNB that has received a report on RSRP measurement results based onan RRM-RS checks an approximate location of a corresponding UE andnotifies the UE of a precoded CSI-RS configuration transmitted toward acorresponding point so that the U can measure a CSI-RS and feeds backCSI (e.g., an RI, a PMI and a CQI) for PDSCH scheduling. Furthermore, aneNB that has received a report on RSRP measurement results based onRRM-RSs transmitted by a plurality of cells determines that acorresponding UE will be handovered to which cell and which precodedCSI-RS will be configured in the UE in a target cell based on the RSRPmeasurement results. That is, RSRP measurement results based on RRM-RSsprovide an eNB with important information necessary to determine thatwhich precoded CSI-RS will be configured in a corresponding UE in thefuture.

If 4-port CSI-RSs are configured in a corresponding UE based on RSRPmeasurement results, such as that in the example of FIG. 12, so that amaximum of 4 data streams can be transmitted or the best beam switchingis rapidly performed in line with a change of fading, it is expectedthat to generate and configure 4-port CSI-RSs having the same beamdirection as RRM-RS ports 13, 24, 25 and 26 having the greatest RSRPwill be optimal. However, overhead is too great if a CSI-RS isoptimized, generated and transmitted for each UE. Accordingly, a methodfor reducing CSI-RS transmission overhead is to allow many UEs in thesame environment to share a CSI-RS. In order to achieve the aboveobject, CSI-RS antenna ports within one CSI-RS configuration may beprecoded to have a characteristic of a beam transmitted in an adjacentdirection. That is, if a 4-port CSI-RS1 having the same beam directionas RRM-RS ports 12, 13, 14 and 15 and a 4-port CSI-RS2 having the samebeam direction as RRM-RS ports 24, 25, 26 and 27 have been previouslyconfigured by taking into consideration different served UEs, whether itis better to configure which CSI-RS in a corresponding UE may bedetermined based on the RSRP report of an RRM-RS.

In another embodiment of the present invention, RSRP is also measuredand reported with respect to an antenna port group. In the proposedmethod, antenna ports are grouped, and RSRP of an antenna port group iscalculated by averaging pieces of RSRP of antenna ports belonging to thecorresponding antenna port group. The group may be previously determinedor an eNB may provide notification of the group. Alternatively, a UE maydetermine a grouping method and report the determined grouping method.

As in the example of FIG. 12, RRM-RSs including 32 ports may be groupedevery 4 ports. The groups may be disjointed and grouped into 8 (=32/4)groups. In this case, an (i)-th port group includes RRM-RS ports (4 i),(4 i+1), (4 i+2), and (4 i+3). RSRP of the (i)-th port group is definedas an average of pieces of RSRP of the antenna ports (4 i), (4 i+1), (4i+2), and (4 i+3).

In yet another embodiment, overlapping between groups may be permitted,and grouping may be performed. If RRM-RSs including 32 ports are groupedevery 4 ports, the RRM-RSs are grouped into 15 groups. In this case, an(i)-th port group includes RRM-RS ports (2 i), (2 i+1), (2 i+2), and (2i+3). If the proposed method is generalized, ports are grouped every Aports and a port interval between adjacent groups is set as B, an (i)-thport group includes RRM-RS ports (B*i), (B*i+1), (B*i+A-1). An eNB maydesignate the setting of the parameters A and B to a UE, or a UE mayselect the setting of the parameters A and B by taking intoconsideration a channel environment and UE capability and report theselected setting.

As a modification of the proposed method, in a method for selecting anantenna port group to be reported, a UE may take into considerationcapabilities which may be obtained through a corresponding antenna portgroup compared to RSRP. In this case, the UE calculates the capabilitiesby taking into consideration multi-layer data transmission from aplurality of antennas within the antenna port group.

Antenna Port Grouping Level

In the proposed method, a plurality of grouping methods having differentsizes may be used. That is, a method for grouping antenna ports every A1ports and a method for grouping antenna ports every A2 ports may be usedat the same time. A method for grouping antenna ports every A_i ports ishereinafter referred to as a “grouping level i.”

FIG. 13 illustrates RRM-RS antenna port grouping levels according to anembodiment of the present invention.

FIG. 13 shows an example of a grouping method performed by applying a4-step grouping level to 16-port RRM-RSs. In the example, the groupinglevel 1 shows a method of grouping antenna ports every port and shows amethod not performing grouping. Furthermore, antenna ports are groupedevery 2 ports, 4 ports and 8 ports in the grouping levels 2, 3 and 4,respectively. In the example of FIG. 13, antenna port groups having thesame level have been illustrated as being disjointed and configured.

In such a multiple grouping method, a UE reports RSRP for each groupinglevel. That is, a UE selects and reports an antenna group having highRSRP for each grouping level. Alternatively, a UE may compare RSRP ofantenna groups having different levels and report a group level comparedto the best group. In order to compare RSRP between antenna groupshaving different levels 1, group RSRP of each level is corrected by aspecific offset and compared. In the case where R RRM-RSs have beenconfigured, if RSRP of the (g)-th antenna port group of the (1)-thgrouping level of an (r)-th RRM-RS is defined as GRSRP(r,l,g),Adj_GRSRP(r,l,g) is calculated by correcting GRSRP(r,l,g) by anoffset(r,l) designated for the (1)-th grouping level of the (r)-thRRM-RS by an eNB as follows and is compared with GRSRP(r,l,g).Adj_GRSRP(r,l,g)=GRSRP(r,l,g)+offset(r,l)  [Equation 15]

In addition, in order to reduce a frequent change in the best L reportedin a method for reporting RSRP of the best L port groups for eachgrouping level or in all of grouping methods, RSRP may be corrected byadding a hysteresis parameter Hy.Adj_GRSRP(r,l,g)=GRSRP(r,l,g)+offset(r,l)±Hy  [Equation 16]

In Equation 16, whether the parameter Hy is to be added or subtracted isdetermined depending on whether a corresponding port group is includedin the best L GRSRP in a previous report. If the corresponding portgroup is included in the best L GRSRP in the previous report, theparameter Hy is added to apply a bias so that high Adj_RSRP is obtained,thereby reducing a frequent change of a port group having the best LAdj_GRSRP.

In a proposed method, a reference antenna port group may be designatedto a UE. An eNB may designate the antenna port groups of a precodedCSI-RS configured in a corresponding UE and an RRM-RS transmitted by aserving cell having the same beam direction as a reference antenna portgroup. A reference antenna port group may be designated in a UE for eachgrouping level. Alternatively, one reference antenna port group may bedesignated in a UE in all of grouping levels. If the (m_0)-th antennaport group of the (l_0)-th grouping level of an (r_0)-th RRM-RS has beendesignated in a UE as a reference antenna port group, the UE performsreporting if Adj_GRSRP of another antenna port group exceeds a specificthreshold compared to Adj_GRSRP of the reference antenna port group.That is, the UE performs reporting when a difference between pieces ofRSRP exceeds a specific threshold in an Adj_GRSRP ratio or dB scaleexpression as follows.Adj_GRSRP(r,l,g)−Adj_GRSRP(r_0,l_0,m_0)>Threshold  [Equation 17]

Alternatively, as a modification of the proposed method, a UE specifiesreference RSRP through a current CSI-RS, compares RRM-RS-based RSRPresults with CSI-RS-based RSRP, and selects and reports the resultingRSRP.

RRM-RS for 3-Dimension (3-D)

The aforementioned method proposed according to an embodiment of thepresent invention may be modified and applied if the directivity of abeam is expanded from a 2-D space to a 3-D space. The directivity of abeam on the 3-D space is controlled by the two angles of a top/bottomangle (or vertical angle) and a left/right angle (or horizontal angle).Accordingly, in order to check whether an adjacent beam is present, itis efficient to index beams using two indices, that is, a horizontalindex and a vertical index. According to the characteristics of thepresent invention, in order for a beam index and an RRM-RS port index tohave a one-to-one correspondence relation, an RRM-RS port may be indexedwith a horizontal index and a vertical index.

In the case of a 3D MIMO system having M_v beams in the verticaldirection and M_h beams in the horizontal direction, a total of(M_v×M_h) beams are possible. In an embodiment of the present invention,an (M_v×M_h)-port RRM-RS is configured and a horizontal index j_h(j_h=0, M_h-1) and a vertical index j_v(j_v=0, M_v-1) are assigned toeach antenna port. One-dimension index i (i=0, M_v×M_h-1) and 2-Dindices j_h and j_v are assigned to each antenna port by taking intoconsideration the resource mapping of the (M_v×M_h)-port RRM-RS. Thereis a relation “(i)=f(j_h, j_v).”

FIG. 14 is a diagram illustrating antenna ports and antenna port groupsof RRM-RSs arrayed in 2-D indices according to an embodiment of thepresent invention.

Referring to FIG. 14, each of antenna ports is indexed with (j_h, j_v).If antenna ports are grouped every A_h×A_v ports by applying the methodproposed by an embodiment of the present invention and a port intervalbetween adjacent groups is set as B_h and B_v, an (i_h, i_v)-th portgroup includes RRM-RS ports (B_h×i_h+j_h, B_v×i_v+j_v), (j_h=0, . . . ,A_h-1), (j_v=0, . . . , A_v-1). An eNB may designate the setting of theparameters A_h, A_v and B_h, B_v for a UE, or a UE may select thesetting of the parameters by taking into consideration a channelenvironment and UE capability and report the selected setting.

Difference Between RRM-RS and CSI-RS

In the existing LTE/LTE-A system, a CSI-RS is transmitted for thepurpose of a CSI report. A UE reports a RI, a PMI and/or CQI as CSI. Insome cases, the RRM-RS proposed by the present invention is used tomeasure RSRP for each antenna port. It may be better to use resources inwhich an existing CSI-RS can be configured rather than newly definingresources in which the RRM-RS is transmitted. The reason for this isthat transmission efficiency of legacy UEs is not deteriorated. If theRRM-RS is transmitted in a new resource, the legacy UEs do not recognizethe RRM-RS. As a result, transmission efficiency is deteriorated in asubframe in which the RRM-RS is transmitted or the RRM-RS is notscheduled. Accordingly, in a method for sending the RRM-RS usingresources in which the existing CSI-RS can be configured, a CSI-RSincluding a corresponding resource is configured in a legacy UE and thelegacy UE may be notified that data is not mapped to the correspondingresource.

Data is not mapped to a plurality of CSI-RSs configured in a UE for aCSI report. That is, a PDSCH is mapped to the plurality of CSI-RSs otherthan an RE to which the CSI-RS is mapped. In the proposed methodaccording to an embodiment of the present invention, as in the CSI-RS, aPDSCH may be mapped to the RRM-RS other than an RE to which the RRM-RSis mapped. In a modified method, however, a PDSCH may be mapped to theRRM-RS regardless of the RRM-RS. In this case, a UE needs to be able toreceive the RRM-RS and the PDSCH in the same RE at the same time.Alternatively, in order to guarantee the safe reception of the RRM-RS,an eNB may configure a corresponding resource as a ZP-CSI-RS so that aPDSCH is not mapped to the RRM-RS.

QCL Configuration of RRM-RS

If each cell sends an RRM-RS, the configuration of the RRM-RSstransmitted by a serving cell and neighboring cells may be designated toa UE. The UE measures a gain according to the beamforming of the servingcell and a gain according to the beamforming of the neighboring cells,and reports the measured gains to a network so that the gains are usedas a criterion for determining handover. The RRM-RS may be insufficientfor the tracking purpose of a signal because it has very lowtransmission density. Accordingly, tracking results are used to track asignal reliably received with high density, representatively, a CRS andto detect an RRM-RS. That is, the tracking results of the CRS of aserving cell are not suitable for being used for an RRM-RS transmittedby a neighboring cell due to an error in the oscillator which generatesthe carrier frequency of the serving cell and the neighboring cell.Accordingly, notification is provided of a quasi co-located (QCL) CRS(or another specific CS, such as a CSI-RS) that will be used to detectan RRM-RS for each RRM-RS. A UE uses the large-scale property propertiesof a channel, estimated from a QCL CRS (or another specific CS, such asa CSI-RS), to detect an RRM-RS. In this case, the large-scale propertiesof the channel may include one or more of delay spread, Doppler spread,a Doppler shift, an average gain, and average delay.

Extension to RSRQ

The proposed methods according to the embodiments of the presentinvention may be extended and applied to a method for measuring RSRQ foreach antenna port of an RRM-RS. RSRQ is defined as a ratio of RSRP andan RSSI. Accordingly, the measurement of RSSI is added. The measurementresource of the RSSI may be identically configured in all of RRM-RSshaving the same carrier frequency, that is, all of RRM-RSs configured inthe same component carrier. In this case, the results of a comparisonbetween the ports of RRM-RSs within the same component carrier are thesame although RSRP or RSRQ is used. However, a comparison between theports of RRM-RSs within heterogeneous same component carriers isdifferent depending on whether RSRP or RSRQ is used. Accordingly, an eNBdesignates whether RSRP or RSRQ will be used in a UE when the UEperforms an RRM report based on an RRM-RS.

In some cases, each RSSI measurement resource may be separatelyconfigured in an RRM-RS. In this case, a comparison between the ports ofRRM-RSs is different even within the same component carrier depending onwhether RSRP or RSRQ will be used. Accordingly, an eNB designateswhether RSRP or RSRQ will be used in a UE when the UE performs an RRMreport based on an RRM-RS.

Association Between RRM-RS RSRP and CRS RSRP

RSRP based on an RRM-RS according to an embodiment of the presentinvention has an object of incorporating the beamforming gain of an eNBhaving multiple antennas into the selection of a serving cell. Althougha specific neighboring cell has been determined to have the bestbeamforming based on the RSRP of an RRM-RS, if channels broadcasted by acorresponding cell, that is, a channel in which CRS-based demodulationis performed, is not stably received, the handover of a UE to thecorresponding neighboring cell cannot be performed. Accordingly, areport regarding whether both an RRM-RM and a CRS transmitted by aspecific eNB have better quality needs to be received from a UE, and ahandover determination and beam election need to be performed based onthe report. To this end, the UE reports RSRP of the j-th antenna port orport group of an i-th RRM-RS configured in the UE and also reports RSRPof a CRS connected to the i-th RRM-RS. In this case, the CRS connectedto the RRM-RS may be a CRS QCL-subjected to the RRM-RS.

Hereinafter, a CSI measurement and reporting operation method forreducing latency will be described.

A method described below may be extended and applied to systemsincluding 3D-MIMO, massive MIMO, and the like and an amorphous cellenvironment, and the like.

First, the 3D-MIMO system will be described in brief.

The 3D-MIMO system is one of an optimal transmission scheme suitable forthe single-cell 2D-adapative antenna system (AAS) base stationillustrated above in FIG. 11 based on LTE standard (Rel-12) and thefollowing operation may be considered.

As illustrated in FIG. 11, when the 3D-MIMO system is described with anexample of configuring CSI-RS ports from an 8-by-8 (8×8) antenna array,one precoded CSI-RS port to which ‘UE-dedicated beam coefficients’optimized for a specific target UE is applied is configured with respectto each of 8 antennas vertically to configure/transmit a total of 8-port(vertically precoded) CSI-RS horizontally.

Therefore, the UE may perform CSI feedback for 8 ports in the relatedart.

Consequently, the base station transmits CSI-RS 8 ports to which avertical beam gain optimized for individual UEs (alternatively, specificUE group) is already applied (precoded) to the UE.

Therefore, since the UE measures the CSI-RS that undergoes the radiochannel, even though the UE performs the same feedback scheme using aconventional horizontal codebook, the UE may already obtain a verticalbeam gain effect of the radio channel through the CSI measurement andreporting operation for the vertically precoded CSI-RS.

In this case, a method for determining vertical beams optimized forindividual UEs includes (1) a method using an RRM report result by a(vertically precoded) small-cell discovery RS (DRS), (2) a method inwhich the base station receives the sounding RS (SRS) of the UE in anoptimal reception beam direction and converts the correspondingreception beam direction into a DL optimal beam direction by channelreciprocity and applies the DL optimal beam direction, and the like.

When the base station determines that the UE-dedicated best V-beamdirection is changed due to the mobility of the UE, the base stationreconfigures all RRC configurations related with the CSI-RS and anassociated CSI process by the convention operation.

When an RRC reconfiguration process needs to be performed as such,RRC-level latency (e.g., by the unit of several tens to several hundredsof ms) inevitably occurs.

That is, in terms of the network, a target V-beam direction is dividedinto, for example, four in advance and a separate 8-port CSI-RS havingprecoding in each V-direction is transmitted at the correspondingseparate transmission resource location.

Further, since teach UE needs CSI measurement and reporting for onespecific CSI-RS configuration among 8 port CSI-RSs, each UE cannot butperform an RRC reconfiguration procedure with the network by a CSI-RSconfiguration to be changed when the target V-direction is changed.

2D Planar Antenna Array Model

FIG. 15 is a diagram illustrating one example of a polarization based 2Dplane antenna array model.

That is, FIG. 15 illustrates one example of a 2D active antenna system(AAS) having cross polarization.

Referring to FIG. 15, the 2D planar antenna array model may berepresented as (M, N, P).

Herein, M represents the number of antenna elements having the samepolarization in each column, N represents the number of horizontalcolumns, and P represents the number of dimensions of the polarization.

In FIG. 15, in the case of cross-polarization, P=2.

FIG. 16 is a diagram illustrating one example of a transceiver units(TXRUs) model.

A TXRU model configuration corresponding to the antenna array modelconfiguration (M, N, P) of FIG. 15 may be represented as (MTXRU, N, P).

In this case, the MTXRU means the number of TXRUs which exist in thesame 2D column and the same polarization and MTXRU<=M is continuouslysatisfied.

Further, a TXRU virtualization model is defined by a relationship of thesignal of the TXRU and the signals of the antenna elements.

Herein, q represents transmission signal vectors of M antenna elementshaving the same polarization in the same column, w and W represent awideband TXRU virtualization weight vector and a matrix, and xrepresents signal vectors of MTXRU TXRUs.

In detail, FIG. 16a illustrates a TXRU virtualization model option-1(sub-array partition model) and FIG. 16b illustrates a TXRUvirtualization model option-2 (full connection model).

That is, the TXRU virtualization model is divided into the sub-arraymodel, the full-connection model, and the like as illustrated in FIGS.16a and 16b according to a correlation between the antenna elements andthe TXRU.

Further, mapping of the CSI-RS ports and the TXRUs may be 1-to-1 or1-to-many.

Codebook Based Precoding Technique

Precoding that appropriates distributes transmission information torespective antennas according to the channel situation, and the like maybe adopted in order to support multi-antenna transmission.

The codebook based precoding technique represents a technique thatpredetermines a set of precoding matrixes in the transmitting side andthe receiving side, feeds back to the transmitting side which matrix themost appropriate precoding matrix is by measuring the channelinformation from the transmitting side (e.g., the base station) by thereceiving side (e.g., the UE), and applies the appropriate precoding tosignal transmission based on the PMI by the transmitting side.

Since the codebook based precoding technique is a technique that selectsthe appropriate matrix in the predetermined set of precoding matrixes,the optimal precoding is not continuously applied, but feedback overheadmay be reduced as compared with a technique that explicitly feeds backthe optimal precoding information to the actual channel information.

FIG. 17 is a diagram for describing a basic concept of codebook basedprecoding.

According to the codebook based precoding technique, the transmittingside an the receiving side share codebook information including apredetermined number of precoding matrixes according to a transmissionrank, the number of antennas, and the like. That is, when feedbackinformation is infinite, the codebook based precoding technique may beused. The receiving side measures the channel state through the receivedsignal to feed back an infinite number of preferred precoding matrixinformation (that is, an index of the corresponding precoding matrix) tothe transmitting side based on the codebook information. For example,the receiving side measures the received signal by a maximum likelihood(ML) or minimum mean square error (MMSE) technique to select the optimalprecoding matrix. It is illustrated that the receiving side transmits tothe transmitting side the precoding matrix information for eachcodeword, but the present invention need not be limited thereto.

The transmitting side that receives the feedback information from thereceiving side may select a specific precoding matrix from the codebookbased on the received information. The transmitting side that selectsthe precoding matrix may perform the precoding by a method thatmultiplies layer signals of a number corresponding to the transmissionrank by the selected precoding matrix and transmit the transmittedsignal of which precoding is performed to the receiving side through aplurality of antennas. In the precoding matrix, the number of rows isthe same as the number of antennas and the number of columns is the sameas a rank value.

Since the rank value is the same as the number of layers, the number ofcolumns is the same as the number of layers. For example, when thenumber of transmission antennas is 4 and the number of transmissionlayers is 2, the precoding matrix may be configured by a 4×2 matrix.Information transmitted through the respective layers may be mapped tothe respective antennas through the precoding matrix.

The receiving side that receives the signal precoded and transmitted bythe transmitting side performs inverse processing of the precodingperformed by the transmitting side to restore the received signal. Ingeneral, the precoding matrix satisfies a unitary matrix (U) conditionsuch as U*U^(H)=I, therefore, the inverse processing of the precodingmay be performed by multiplying the received signal by Hermit matrixP^(H) of the precoding matrix P used for the precoding of thetransmitting side.

For example, Table 8 given below shows a codebook used in downlinktransmission using 2 transmission antennas in 3GPP LTE release-8/9 andTable 9 shows a codebook used in downlink transmission using 4transmission antennas in the 3GPP LTE release-8/9.

TABLE 8 Codebook Number of layers υ index 1 2 0$\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\1\end{bmatrix}$ $\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}$ 1 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 1 \\1 & {- 1}\end{bmatrix}$ 2 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 1 \\j & {- j}\end{bmatrix}$ 3 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- j}\end{bmatrix}$ —

TABLE 9 Codebook Number of layers υ index u_(n) 1 2 3 4 0 u₀ = [1 −1 −1−1]^(T) W₀ ^({1}) W₀ ^({14})/√{square root over (2)} W₀^({124})/√{square root over (3)} W₀ ^({1234})/2 1 u₁ = [1 −j 1 j]^(T) W₁^({1}) W₁ ^({12})/√{square root over (2)} W₁ ^({123})/√{square root over(3)} W₁ ^({1234})/2 2 u₂ = [1 1 −1 1]^(T) W₂ ^({1}) W₂ ^({12})/√{squareroot over (2)} W₂ ^({123})/√{square root over (3)} W₂ ^({3214})/2 3 u₃ =[1 j 1 −j]^(T) W₃ ^({1}) W₃ ^({12})/√{square root over (2)} W₃^({123})/√{square root over (3)} W₃ ^({3214})/2 4 u₄ = [1 (−1 −j)/√{square root over (2)} −j (1 − j)/√{square root over (2)}]^(T) W₄^({1}) W₄ ^({14})/√{square root over (2)} W₄ ^({124})/√{square root over(3)} W₄ ^({1234})/2 5 u₅ = [1 (1 − j)/√{square root over (2)} j (−1 −j)/√{square root over (2)}]^(T) W₅ ^({1}) W₅ ^({14})/√{square root over(2)} W₅ ^({124})/√{square root over (3)} W₅ ^({1234})/2 6 u₆ = [1 (1 +j)/√{square root over (2)} −j (−1 + j)/√{square root over (2)}]^(T) W₆^({1}) W₆ ^({13})/√{square root over (2)} W₆ ^({134})/√{square root over(3)} W₆ ^({1324})/2 7 u₇ = [1 (−1 + j)/√{square root over (2)} j (1 +j)/√{square root over (2)}]^(T) W₇ ^({1}) W₇ ^({13})/√{square root over(2)} W₇ ^({134})/√{square root over (3)} W₇ ^({1324})/2 8 u₈ = [1 −1 11]^(T) W₈ ^({1}) W₈ ^({12})/√{square root over (2)} W₈ ^({124})/√{squareroot over (3)} W₈ ^({1234})/2 9 u₉ = [1 −j −1 −j]^(T) W₉ ^({1}) W₉^({14})/√{square root over (2)} W₉ ^({134})/√{square root over (3)} W₉^({1234})/2 10 u₁₀ = [1 1 1 −1]^(T) W₁₀ ^({1}) W₁₀ ^({13})/√{square rootover (2)} W₁₀ ^({123})/√{square root over (3)} W₁₀ ^({1324})/2 11 u₁₁ =[1 j −1 j]^(T) W₁₁ ^({1}) W₁₁ ^({13})/√{square root over (2)} W₁₁^({134})/√{square root over (3)} W₁₁ ^({1324})/2 12 u₁₂ = [1 −1 −11]^(T) W₁₂ ^({1}) W₁₂ ^({12})/√{square root over (2)} W₁₂^({123})/√{square root over (3)} W₁₂ ^({1234})/2 13 u₁₃ = [1 −1 1−1]^(T) W₁₃ ^({1}) W₁₃ ^({13})/√{square root over (2)} W₁₃^({123})/√{square root over (3)} W₁₃ ^({1324})/2 14 u₁₄ = [1 1 −1−1]^(T) W₁₄ ^({1}) W₁₄ ^({13})/√{square root over (2)} W₁₄^({123})/√{square root over (3)} W₁₄ ^({3214})/2 15 u₁₅ = [1 1 1 1]^(T)W₁₅ ^({1}) W₁₅ ^({12})/√{square root over (2)} W₁₅ ^({123})/√{squareroot over (3)} W₁₅ ^({1234})/2

In Table 9 given above, W_(n) ^({s}) is obtained as a set {s} configuredfrom an equation expressed like=W_(n)=I−2u_(n)u_(n) ^(H)/u_(n)^(H)u_(n). In this case, I represents a 4×4 unitary matrix and u_(n)represents a value given in Table 7.

As shown in Table 8 given above, the codebook for 2 transmissionantennas has a total of 7 precoding vectors/matrixes and herein, sincethe unitary matrix is used for an open-loop system, the total number ofprecoding vectors/matrixes for precoding of a close-loop system becomes6. Further, the codebook for 4 transmission antennas shown in Table 7given above has a total of 64 precoding vectors/matrixes.

The codebooks have common properties including a constant modulus (CM)property, a nested property, a constrained alphabet, and the like. Inthe case of the CM property, respective elements of all precodingmatrixes in the codebook do not include ‘0’ and are configured to havethe same size.

The nested property means that the precoding matrix having a low rank isdesigned to be configured by subsets of a specific column of theprecoding matrix having a high rank. The constrained alphabet propertymeans a property in which alphabets of the respective elements of allprecoding matrixes in the codebook are configured by

$\left\{ {{\pm 1},{\pm j},{\pm \frac{\left( {1 + j} \right)}{\sqrt{2}}},{\pm \frac{\left( {{- 1} + j} \right)}{\sqrt{2}}}} \right\}.$

Feedback Channel Structure

Basically, since the base station may not know information on a downlinkchannel in a frequency division duplex (FDD) system, the channelinformation which the UE feeds back is used for the downlinktransmission. In the existing 3GPP LTE release-8/9 system, the UE mayfeed back the downlink channel information through the PUCCH or feedback the downlink channel information through the PUSCH. In the case ofthe PUCCH, the channel information is fed back periodically and in thecase of the PUSCH, the channel information is fed back aperiodicallyaccording to a request of the base station. Further, in the case of thefeedback of the channel information, the channel information for a wholefrequency band (that is, wideband (WB)) may be fed back and the channelinformation may be fed back with respect to a specific number of RBs(that is, subband (SB)).

Codebook Structures

As described above, since the transmitting side and the receiving sideshare a pre-defined codebook to reduce overhead which occurs so as forthe receiving side to feed back the precoding information to be used forMIMI transmission from the transmitting side, efficient precoding may beadopted.

As one example of configuring the pre-defined codebook, a precodermatrix may be configured by using a discrete Fourier transform (DFT)matrix or a Walsh matrix. Alternatively, the precoder matrix is combinedwith a phase shift matrix or a phase shift diversity matrix to configurevarious types of precoders.

In a co-polarization antenna series, DFT-series codebooks are excellentin performance and herein, in configuring the DFT matrix based codebook,an n×n DFT matrix may be defined as shown in Equation 18 given below.

$\begin{matrix}{{{{DFTn}\text{:}\mspace{14mu}{D_{n}\left( {k,l} \right)}} = {\frac{1}{\sqrt{n}}{\exp\left( {- \frac{j\; 2\pi\;{kl}}{n}} \right)}}},k,{l = 0},1,\ldots\mspace{14mu},{n - 1}} & \left\lbrack {{Equation}\mspace{14mu} 18} \right\rbrack\end{matrix}$

In the case of the DFT matrix of Equation 18 given above, only onematrix exists with respect to a specific size n. Therefore, in order todefine various precoding matrixes and appropriately use the definedprecoding matrixes according to a situation, it may be considered that arotated version of a DFTn matrix is additionally configured and used.Equation 19 given below shows an exemplary rotated DFTn matrix.

$\begin{matrix}{{{{rotated}\mspace{14mu}{DFTn}\text{:}\mspace{14mu}{D_{n}^{({Gg})}\left( {k,l} \right)}} = {\frac{1}{\sqrt{n}}{\exp\left( {- \frac{j\; 2\;\pi\;{k\left( {1 + \frac{g}{G}} \right)}}{n}} \right)}}},\mspace{20mu} k,{l = 0},1,\ldots\mspace{14mu},{n - 1},{g = 0},1,\ldots\mspace{14mu},G} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

When the DFT matrix is configured as shown in Equation 19 given above, Grotated DFTn matrixes may be generated and the generated matrixessatisfy the property of the DFT matrix.

Accordingly, hereinafter, the CSI measurement and reporting method forremoving or significantly reducing the RRC-level latency will bedescribed in detail.

That is, a method described below relates to a method that allocatesonly a single CSI process and a single uplink (UL) feedback resource tothe UE and indicates what a CSI-RS index (and/or CSI-IM index) to bemeasured is at not the RRC level but the MAC level (alternatively, PHYlevel).

The MAC CE may be used for the MAC level indication and the DCI may beused for the PHY level indication.

That is, in the method described below, the base station (alternatively,network) configures the CSI-RS configurations for multiple candidateCSI-RSs by using the RRC signaling and explicitly or implicitlyannounces an ‘activation’ indication for at least one CSI-RS in whichthe CSI-RS measurement and reporting are performed among the multiplecandidate CSI-RSs to the UE.

For example, when CSI-RS 1 is activated, in a situation in which it isconsidered whether CSI-RS 1 is transferred to CSI-RS 2, the base stationmay first indicate pre-activation to the UE so as to track CSI-RS 2before actually indicating a reactivate command to transfer CSI-RS 1 toCSI-RS 2.

Herein, the tracking of the CSI-RS may mean an operation of time and/orfrequency synchronization with respect to the CSI-RS so as for the UE tomeasure the CSI-RS.

That is, pre-activated CSI-RS X may be actually activated or notactivated (within a specific timer time).

Herein, the UE may feed back intact CSI reporting to the base stationwithin specific y ms after receiving an activation message indicatingactivation of the CSI-RS x from the base station.

Herein, feeding back the intact CSI reporting may be construed as a casewhere the UE performs meaningful CSI feedback to the base station.

It may be determined whether the CSI feedback is meaningful ormeaningless according to the number of measured samples.

Transmission of Capability Information

In more detail, in the present specification, first, the UE transmits aspecific capability signaling to the base station announces capabilityinformation related with the CSI operation thereof to the base stationin advance (e.g., upon initial connection).

The capability information of the UE related with the CSI operation mayinclude at least one of information given below.

Herein, the CSI related operation (alternatively, CSI operation related)may mean operations related with the CSI-RS, the CSI-IM, and/or the CSIprocess.

A disclosure of ‘A and/or B’ may be construed as ‘at least one of A andB’.

1. Capability Information Regarding the Maximum Number of (Nc) CSI-RSs,(Ni) CSI-Interference Measurements (IMs), and/or (Np) CSI Processeswhich May be Simultaneously Fully Activated

Herein, an expression of ‘full activation (configuration)’ means thatthe base station may actually simultaneously configure all of a total ofNC (=3) CSI-RSs, Ni (=3) CSI-IMs, and Np (=4) processes in the case ofthe UE in which Nc=3, Ni=3, and Np=4 and in this case, all CoMPoperations in the convention Rel-11 standard may be supported.

That is, the full activation means that the UE needs to perform channelmeasurement with respect to all of Nc=3 CSI-RSs, interferencemeasurement (IM) with respect to all of Ni=3 CSI-IMs, and CSI feedbackwith respect to Np=4 CSI processes.

2. Capability Information Regarding the Maximum Number of (Nc′) CSI-RSs,(Ni′) CSI-Interference Measurements (IMs), and/or (Np′) CSI Processeswhich May be Simultaneously Partially Activated

Herein, an expression of ‘partial activation’ may be limited only tospecific some operations (e.g., CSI-RS tracking) among the operationswhich may be performed by the UE upon the ‘full activation’ or include aseparate additional operation.

For example, in the case of the specific UE, parameters in Term 1 givenabove may show Nc=1, Ni=1, and Np=1 and simultaneously, the parametersin Term 2 given above may show Nc′=3, Ni′=1, and Np′=1.

That is, there is only a difference in that Nc=1 and Nc′=3.

This meaning may be construed as a meaning that the specific UE maymaintain time/frequency synchronization/tracking with respect to Nc′(=3) partially activated CSI-RSs and may be designated with Nc (=1)specific ‘fully activated’ CSI-RS among the three CSI-RSs.

A representative method which may be designated with Nc (=1) CSI-RS mayinclude (1) a method that may receive an indication in the MAC layerthrough an MAC CE command, and the like, (2) a method that may receive amore dynamic indication in the PHY layer through the DCI signaling, andthe like.

Since the UE may just perform only single CSI feedback (in a specificCC) for Np=Np′ (=1) CSI process through such a method, complexity andoverhead of the CSI feedback may be continuously similarly maintained.

In addition, there is an advantage that only the CSI-RS index which theUE needs to measure may be dynamically switched through the signaling ofthe MAC layer or PHY layer through the method proposed in the presentspecification.

That is, the present specification provides a method that switches onlya resource to be measured by the RRC signaling, that is, through asignaling having latency smaller than the CSI-RS reconfigurationlatency.

In the present specification, for easy description, the CSI-RS isprimarily described, but it is apparent that the method proposed in thepresent specification may be similarly extended and applied even todynamic switching of the CSI-IM index (alternatively, CSI processindex).

Additionally, there may be an additional restriction in the form ofNc<=Nc′, Ni<=Ni′, and/or Np<=Np′ among the parameters in Terms 1 and 2given above.

In this case, the UE needs to transmit the capability signaling as longas such a condition is satisfied.

When the base station receives from the UE the capability signalingincluding the capability information of the UE related with the CSIoperation, the base station needs to transmit the RRC signaling to theUE in such a manner not to violate the capability property combinationat the time of configuring the corresponding UE later.

The UE does not expect a case in which the capability property isviolated and may regard the case as an error case.

As described above, it is assumed that the UE may be configured with allof three CSI-RSs corresponding to Nc′=3 from the base station throughthe RRC signaling.

However, in this case, the UE may receive from the base station asignaling to recognize that the CSI-RS is configured to the ‘partialactivation’ state for each CSI-RS index by a separate identifier or aspecific implicit indication to identify that the CSI-RS is configuredto the ‘partial activation’ state for each CSI-RS index.

In this case, the UE performs time/frequency synchronization/trackingfor each of the three CSI-RSs from the time of receiving the RRCsignaling.

In this case, the synchronization/tracking may be performed based oninformation such as a specific RS (e.g., CRS), or the like so as toapply a quasi co-location (QCL) assumption included in the each CSI-RSconfiguration.

In this case, it may be additionally (alternatively, simultaneously)configured or indicated that only Nc (=1) specific CSI-RS among Nc′ (=3)CSI-RSs is ‘fully activated’ in the form of the separate identifier.

Alternatively, implicitly, Nc (=1) CSI-RS may be pre-defined as aspecific index, such as continuosly defining the CSI-RS as a lowest(highest) indexed CSI-RS.

Then, the UE may perform the channel measurement for the CSI feedbackonly with respect to Nc (=1) ‘full activated’ CSI-RS.

That is, the UE performs only the tracking without performing thechannel measurement with respect to Nc′−Nc=2 remaining CSI-RSs.

As such, in a method that performs the channel measurement only withrespect to Nc=1 specific CSI-RS and derives feedback contents (e.g.,RI/PMI/CQI) through the measurement, an operation of calculating thefeedback contents with respect to a specific CSI process configuredtogether with the CSI-RS may be defined/configured.

For example, the UE receives even Np=1 specific CSI process from thebase station through the RRC signaling and the CSI process is defined asa combination between a specific number of CSI-RSs and the CSI-IM index.

However, herein, in the case of the CSI-RS, an operation may bedefined/configured, which automatically reflects the fully activatedCSI-RS according to what Nc=1 fully activated CSI-RS is to recognize thecorresponding CSI-RS as a CSI-RS which becomes a target of the channelmeasurement of the corresponding CSI process.

As another example, for example, Np′=3 CSI processes may be configuredas the partial activation state and Nc′=3 CSI-RS indexes in therespective CSI processes may be configured.

Thereafter, the base station may dynamically indicate Np=1 specificfully activated CSI process to the UE through the MAC or PHY signaling.

Then, the UE may transmit the CSI feedback for the specific fullyactivated CSI process to the base station.

Consequently, a separate identifier or specific implicit signalingmethod may be defined, which may identify whether the specific CSI-RSand/or CSI-IM index indicated in link with the specific CSI process is afixed index or an automatically variable index for each specific CSIprocess.

When the specific CSI-RS and/or CSI-IM index is fixed and indicated asthe specific index, the UE performs measurement of resourcescorresponding to the fixed CSI-RS and/or CSI-IM index.

When the specific CSI-RS and/or CSI-IM index is configured as thevariable index type, in the case where Nc=1 CSI-RS is ‘fully activated’through the separate MAC or PHY signaling as described above, thecorresponding index may be automatically applied.

Herein, the number of fully activated Ncs may be two or more.

For example, the number of fully activated Ncs may be two or more in acase such as a purpose of measuring multiple CSI-RS resources in the2D-AAS structure through a Kronecker operation, and the like.

Even in this case, what fully activated Ncs are is separatelydynamically indicated, the indexes may be automatically applied.

Consequently, in which candidate set the CSI-RS and/or CSI-IM indexwhich may be indicated in the corresponding configuration may beconfigured may be preferably defined from the RRC configuration step inthe CSI process configuration.

Similarly, it is apparent that the configuration or indication operationdepending on the numbers of Ni's and Nis may be applied even to theCSI-IM.

FIG. 18 is a diagram illustrating one example of a method for measuringand reporting CSI.

Referring to FIG. 18, the UE transmits the capability signalingincluding the capability information of the UE related with the CSIoperation to the base station (S1810).

The capability information of the UE includes first control informationrepresenting the maximum number of CSI related operations which may besimultaneously fully activated and second control informationrepresenting the maximum number of CSI related operations which may besimultaneously partially activated.

Thereafter, when the configuration related with the CSI operation ischanged, the base station transmits CSI operation related configurationinformation (alternatively, CSI related operation configurationinformation) to the UE (S1820).

The CSI operation related configuration information includes at leastone of partial activation CSI related operation index informationrepresenting a CSI related operation of performing the partialactivation and full activation CSI related operation index informationrepresenting a CSI related operation of performing the full activation.

Thereafter, the UE measures the full activated CSI based on the CSIoperation related configuration information (S1830).

Before step S1830, the UE performs the tracking with respect to thepartially activated CSI-RS.

The CSI-RS tracking is described in detail with reference to the abovecontents.

Thereafter, the UE reports the measurement result to the base station(S1840).

FIG. 19 is a diagram illustrating another example of the method formeasuring and reporting CSI.

Since S1910 and S1920 and S1940 and S1950 are the same as S1810 toS1840, a detailed description thereof will be omitted.

After step S1920 (after the base station transmits the CSI operationrelated configuration information to the UE), the base station transmitsan indication message of indicating measurement for the fully activatedCSI-RS to the UE (S1930).

The indication message may be MAC CE or DCI.

Further, the fully activated CSI-RS may be preferably selected from thepartially activated CSI-RSs.

CSI Measurement Window Initialization/Update Time

When the UE receives the fully activated signaling of the specificCSI-RS, CSI-IM, and/or CSI process index(es) from the base stationthrough the MAC signaling or PHY signaling at a subframe (SF) # n time,the UE may apply CSI measurement and reporting to be performed fromspecific y ms, that is, SF #(n+y) time from the corresponding time(subframe # n).

In the case of the periodic CSI reporting, CSI measurement and reportingfor specific CSI-RS, CSI-IM, and/or CSI process index(es) which arenewly fully activated starts from a specific reference resource timelinked with an RI reporting instance which is output first after the SFSF #(n+y) time.

That is, with respect to valid reference resource times which existafter the SF #(n+y) time, the CSI (e.g., RI/PMI/CQI) calculated at thereference resource time may be defined to report new CSI contents fromthe time when the RI is initially reported.

That is, before the initial RI reporting time, even though the PMI/CQIreporting instance exists, the CSI feedback contents based on not thenewly full activated configuration but the configuration which isfollowed just before the first RI reporting time need to be continuouslyreported.

Consequently, the CSI reporting of the UE is performed based on thefully activated configuration from the new RI reporting instance time.

In the above operations, configuration information related with a windowthat averages the CSI measurement may be defined to be provided throughthe RRC signaling separately or together.

Further, such an operation may be defined only with respect to anenhanced UE that supports a configuration of a type such as thefull/partial activation.

That is, conventional unrestricted observation is not permitted but themeasurement is averaged only in a specific [d1, d2] ms time interval.

The reason is that since the resource configuration information of theCSI-RS and/or CSI-IM to be measured may be dynamically switched throughthe MAC or PHY signaling, the measurement averaging may be preferablydefined to be performed only within a specific bounded interval.

As one example, when the UE receives a signaling in which the resourceconfiguration information of the CSI-RS and/or CSI-IM to be measured isdynamically switched/indicated through the MAC or PHY signaling (e.g.,by DCI), the UE may be defined/configured to initialize or update themeasurement averaging window of the CSI-RS-based channel measurement inlink with the signaling.

Further, the UE may initialize or update the measurement averagingwindow of the corresponding CSI-IM-based interference measurement inlink with the (dynamically switched/indicated) signaling.

Herein, initializing or updating the measurement averaging window meansinitializing or updating a ‘start point of the measurement window’called the ‘from the predetermined time’ again from # n (alternatively,after a specific configured/indicated time, e.g., # n+k), the time ofreceiving the (dynamically switched/indicated) signaling instead of, forexample, a conventional operation of averaging channel measurementvalues from the corresponding CSI-RS ports, which are repeatedlymeasured up to now from a predetermined past time according to a UEimplementation by ‘unrestricted observation’ for CSI measurementaccording to a current standard.

Alternatively, a scheme that explicitly signals time information (e.g.,timestamp type) representing from which time the correspondingmeasurement window is initialized or updated together may also beapplied.

For example, the scheme may include a time information indicating methodfor absolute time parameter values including SFN, slot number, and thelike or a scheme that indicates the signaling in a specific +/−Deltavalue type from the time when the UE receives the signaling.

In other words, it may be limited that the signaling serves toupdate/reset only the start time of only the measurement averagingwindow.

Then, the UE may average the CSI measurement values (according to the UEimplementation) until the additional signaling is received after thecorresponding time.

The signaling may be separately (independently) signaled for each CSIprocess. Therefore, the measurement window reset may be independentlyapplied for each process.

The signaling may be together applied even for a purpose of resettingthe interference measurement averaging window for the specific CSI-IMresource.

In this case, the signaling serves to initialize the measurementaveraging window for the CSI-RS and the CSI-IM which belong to thespecific CSI process.

Alternatively, a scheme that signals a separate (independent) indicatorfor resetting the interference measurement averaging window for theCSI-IM resource may also be applied.

This announces the UE to initialize the measurement averaging window forthe specific CSI process so as to separate a past interferenceenvironment not to be reflected to the interference measurement valuefrom a current time any longer, for example, when an interferenceenvironment which may be predicted/sensed by the base station is changedin an environment (e.g., eICIC, eIMTA, LAA, and the like) in which theinterference environment is changed.

FIG. 20 is a diagram illustrating yet another example of the method formeasuring and reporting CSI.

Since S2010 to 2030, S2050, and S2060 are the same as S1910 to S1930,S1940, and S1950 of FIG. 19, the detailed description thereof will beomitted.

Referring to FIG. 20, after step S2030, the UE initializes or updatesthe CSI measurement window (S2040).

Thereafter, the UE repeatedly measures the fully activated CSI-RSsduring the initialized or updated CSI measurement window interval,averages the measurement result, and reports the average value to thebase station (S2050 and S2060).

Before step S2040, the base station may transmit CSI measurement windowrelated configuration information to the UE.

As yet another embodiment of a similar type to the (dynamicallyswitched/indicated) signaling, the aforementioned measurement windowconfiguration related operation may be applied even to a beamformedCSI-RS based scheme as described below in the present specification.

PMI feedback scenarios given below may be considered for elevationbeamforming and FD-MIMO operations.

1. Precoding definition of EBF(Elevation Beamforming)/FD-MIMO

(1) Precoding matrix/vector

P₁: wideband; updated less frequently

P₂: subband or wideband; updated more frequently

P is a function of P₁ and P₂, applied to 1D or 2D antenna array (Prepresents functions of P₁ and P₂ applied to a 1D or 2D antenna.)

PMI(s) are to be specified w.r.t. the above definition

(2) Scenarios for CSI feedback

Scenario 1

UE measures CSI-RS ports beamformed with P₁(P₁ transparent to UE).

PMI report(s) for P₂

Scenario 2

UE measures non-precoded 1-D or 2-D CSI-RS ports

Note: P₁ not applied to CSI-RS at Enb

PMI report(s) for P₁ and P₂

Scenario 3

UE measures both non-precoded 1- or 2-D CSI-RS ports (lower duty cycle)and CSI-RS beamformed with P₁

PMI report(s) for P₁ and P₂

Scenario 4

UE measures non-precoded 1- or 2-D CSI-RS ports

Note: P₁ not applied to CSI-RS at eNB(P₁ indicated to UE).

PMI report(s) for P₂

Among scenarios 1 to 4, for example, in the method using the beamformedCSI-RS like scenarios 1 and 3, even though the UE need not know matrixP1 itself, when P1 in which the base station applies beamforming to thecorresponding CSI-RS ports is changed, the base station needs toannounce change time related information of the P1 to the UE in advance.

Thus, the UE may configure/apply an appropriate measurement averagingwindow upon CSI measurement and calculation.

That is, according to the current standard, when the UE performs thechannel measurement for the corresponding CSI-RS ports, reliability maybe enhanced by averaging the channel measurement values from thecorresponding CSI-RS ports, which are repeatedly measured up to now fromthe predetermined past time by the ‘unrestricted observation’ (e.g.,noise suppression effect).

However, in scenarios 1 to 4, since the P1 itself uses the beamformedCSI-RS ports which are not known to the UE, the base station may changethe P1 itself at a predetermined time and when the base station does notannounce that the P1 is changed to the UE, the UE may average thechannel measurement values for P1 before the change and P1′ after thechange together, and as a result, a problem may occur in accuracy of thecorresponding CSI measurement and reporting.

Accordingly, the present specification provides a method in which thebase station transmits a kind of ‘beam-change notification’ or‘beam-change indicator (BCI) signaling to the UE in order to solve theproblem.

Hereinafter, ‘beam-change indicator’ will be simply referred to as‘BCI’.

A BCI signaling may be indicated as an RRC signaling type.

However, more preferably, the BCI signaling may be provided as thesignaling through the MAC CE or the dynamic indication through the DCI,and the like.

That is, when the UE receives the BCI signaling, the start point of themeasurement averaging window applied upon CSI derivation in thecorresponding CSI process is updated to a reception time (alternatively,a specific time indicated from the corresponding BCI receiving time or atime of explicit indication by the separate timestamp, and the like) ofthe corresponding BCI signaling.

That is, a scheme that explicitly signals time information (e.g.,timestamp type) representing from which time the correspondingmeasurement window is initialized or updated together with the BCIinformation (alternatively, as associated information) may also beapplied.

For example, the scheme may include a time information indicating methodfor absolute time parameter values including SFN, slot number, and thelike or a scheme that indicates the signaling in a specific +/−Deltavalue type from the time when the UE receives the signaling.

That is, it may be limited that the BCI signaling serves to update/resetonly the start time of only the measurement averaging window.

Then, the UE may average the CSI measurement values (according to the UEimplementation) until an additional BCI is received after thecorresponding time (BCI signaling receiving time).

Consequently, since the UE does not know the updated matrix P1 itself,but receives that the P1 is updated through the BCI, the CSI measurementvalues are newly averaged from the indication time to perform CSIcalculation and reporting (e.g., P1, P2, RI, CQI, and the like) for thecorresponding CSI process with respect to only the CSI-RS ports to whichthe updated P1 is applied.

The BCI may be separately (independently) signaled for each CSI process.

Therefore, the measurement window reset may be independently applied foreach process.

The BCI may be together applied even for a purpose of resetting theinterference measurement averaging window for the specific CSI-IMresource.

In this case, the signaling serves to initialize the measurementaveraging window for the CSI-RS and the CSI-IM which belong to thespecific CSI process.

Alternatively, a scheme that signals a separate (independent) indicatorfor resetting the interference measurement averaging window for theCSI-IM resource may also be applied.

This announces the UE to initialize the measurement averaging window forthe specific CSI process so as to separate a past interferenceenvironment not to be reflected to the interference measurement valuefrom a current time any longer, for example, when an interferenceenvironment which may be predicted/sensed by the base station is changedin an environment (e.g., eICIC, eIMTA, LAA, and the like) in which theinterference environment is changed.

<Proposal Content 1>

Proposal content 1 is contents related with the number of NZP CSI-RSports which may be configured for each CSI process when the FD-MIMOoperation is supported.

When a non-precoded CSI-RS based scheme is considered with respect tothe FD-MIMO operation, the number of NZP CSI-RS ports which may beconfigured for each CSI process may need to increase.

However, in terms of the beamformed CSI-RS based scheme, the number ofbeamformed CSI-RS ports for each CSI-RS resource may be flexible.

The reason is that each NZP CSI-RS port configured for the UE in such asituation may be precoded with respect to multiple TXRUs so that thetotal number of NZP CSI-RS ports configured for the UE is much smallerthan that of the non-precoded CSI-RS based scheme.

Hereinafter, the beamformed CSI-RS based scheme will be described inmore detail by considering such an aspect.

Potential CSI-RS Enhancements

For easy description, RE(k,l,n) is notated and the correspondingnotation represents a location of an RE used for transmitting a k-thsubcarrier, an l-th OFDM symbol, and an n-th CSI-RS port.

When applicability of transmission power sharing for subcarriers in thesame OFDM symbol is considered, it is possible to boot RS transmissionpower in RE(ki,l,ni) and RE(kj,l,nj).

In this case, an ni-th CSI-RS port is transmitted in RE(ki,l,ni) and annj-th CSI-RS port is transmitted in RE(kj,l,nj), and frequency divisionmultiplexing (FDM) is performed between the corresponding transmissions.

The RS power boosting may be additionally used with respect to RStransmission. The reason is that there is no transmission in RE(ki,l,nj)and RE(kj,l,ni).

FIG. 21 is a diagram illustrating one example of 6 DB RS power boostingfor a frequency division multiplexed (FDM) RS.

That is, FIG. 21 illustrates one example of CSI-RS power allocation ontoRE(2,1,15) with respect to the 8-port CSI-RS situation.

In FIG. 21, NZP CSI-RS port 15 is transmitted on RE(2,1,15), but threeother RE(3,1,15), RE(8,1,15), and RE(9,1,15) are muted so as to preventinterference in other NZP CSI-RS ports (ports 17 to 22).

Due to the power muting, remaining power may be additionally allocatedto actual RS transmission in RE(2,1,15) and a boosted power level may bedisclosed as 4Ea and average energy per resource element (EPRE) isrepresented by Ea.

The maximum number of supported CSI-RS ports FDM in one PRB pair becomes4.

(Proposal 1): When an RS power boosting influence is considered, themaximum number of supported CSI-RS ports frequency divisionmultiplex(FDM)ed in one PRB pair needs to become 4.

When even the 16-port CSI-RS resource is considered, the non-precoded 16CSI-RS ports for each CSI-RS resource may be designed while satisfyingthe RS power boosting condition.

Further, 4 FDMed CSI-RS ports and 4 code division multiplex(CDM)edCSI-RS ports may be configured in the CSI-RS resource on the samesubcarrier and are applied to the aforementioned 6 dB CSI-RS powerboosting.

However, when the 32-port or 64-port CSI-RS resource is considered, itmay not be appropriate to design the corresponding non-precoded CSI-RSports while satisfying the RS power boosting restriction.

In this case, all non-precoded CSI-RS ports need to be transmittedsubstantially simultaneously (in one pair of OFDM symbols) so as toprevent important CSI aging.

In respect to the beamformed CSI-RS ports, it is continuouslyappropriate to design 32-port, 64-port, or more CSI-RS configuration.

When the entire CIS-RS port is divided into a pair of ‘port-groups’,each port group have different beamformed CSI-RS ports.

For example, when a total 32-port CSI-RS configuration is considered,the 32-port CSI-RS configuration may be divided into 4 port groups andeach port group includes the 8-port CSI-RS resource (vertical beamformedhaving different target vertical beam weights).

That is, the UE measures a total of 32 CSI-RS ports.

However, the UE first selects the best port group, calculates asubsequent existing short-term CSI, and needs to recognize that thereare 4 port groups in order to perform the feedback based on 8 CSI-RSports in the selected port group.

In relation with the aforementioned type, when the UE is configured witha total of N (e.g., N=32) CSI-RS ports, the UE may be configured with aspecific parameter (alternatively, an implicit signaling structure) todetermine the aforementioned CSI-RS port group.

The UE may know how many port groups a total of N CSI-RS ports aredivided into through the specific parameter.

Herein, a total of N CSI-RS ports may be defined and configured as oneCSI-RS resource and a set of multiple CSI-RS resources may be defined inone CSI process.

Herein, up to a total of 4 CSI processes may be supported and each CSIprocess may be represented by the indexes.

That is, the respective CSI processes may be represented by indexes 0,1, 2, and 3.

Further, a CSI related class type class A: non-precoded CSI-RS and classB: Beamformed CSI-RS) of the UE may be configured for each CSI processas described below.

For example, when a parameter, ‘K’ which is the number of port groups isadditionally provided, a K value (K=4) may be signaled together with anN value (e.g., N=32) representing the total number of RS ports.

Then, 32 CSI-RS ports constitute 4 port groups and each port groupincludes 8 CSI-RS ports.

In more detail, as the above example, it is assumed that N (=32) CSI-RSports are provided to the UE through the RRC signaling, and the like bythe CSI-RS configuration.

In this case, when the parameter of K=4 (CSI-RS port group=4) istogether provided, in the case where N=32 CSI-RS ports are enumerated ina port index order, the UE may implicitly recognize that the port groupis formed by the unit of N/K(=32/4=8) ports from the beginning.

That is, when it is assumed that the CSI-RS port indexes are 1, 2, 3, .. . , 32, port-group #1 is from the CSI-RS port corresponding to index 1up to the CSI-RS port corresponding to index 8, that is, index {1, 2, .. . , 8} ports and port-group #2 is up to index {9, 10, . . . , 16}ports.

In such a manner, the UE may automatically determine how CSI-RS portindexing is configured, which is included in each port group ofport-group #1 to port-group #4.

Such a CSI-RS port indexing method is one example and modificationssimilar to the CSI-RS port indexing method are included in the spirit ofthe present invention, which allow the UE to automatically determine theCSI-RS port indexing in the port group through the modifications.

As described above, in the method in which a total of N CSI-RS ports areclassified into K port groups and N/K CSI-RS ports are configured toexist in each port group, there may be various schemes for allowing theUE to perform the CSI measurement and reporting based on such aconfiguration.

As the first example, in the beamformed CSI-RS based scheme described in<Proposal content 1> given above, the same specific beamforming (e.g.,vertical beamforming) may be applied in each port group.

Accordingly, the UE select the best port group and performs the CSI-RSfeedback for the selected port group.

Herein, the UE may perform the CSI-RS feedback for the selected portgroup during a long term.

Further, the UE may perform short-term CSI-RS feedback for the CSI-RSports in the selected port group.

The CSI-RS reporting method proposed in the present specification may begenerally divided into (1) the non-precoded CSI-RS (reporting) methodand (2) the beamformed CSI-RS (reporting) method.

The non-Precoded CSI-RS method may be performed in the class A type UEand the beamformed CSI-RS may be performed in the class B type UE.

That is, the present invention, it may be construed that the class Atype UE performs a non-precoded CSI-RS related ooperation and the classB type UE performs a beamformed CSI-RS related operation.

As a second example, as described in <Proposal content 2> to bedescribed below, even in the precoded CSI-RS based scheme, the UEoperation under the aforementioned port group based signaling structuremay be defined/configured.

For example, when the UE is allowed to perform the CSIderivation(alternatively, calculation) in a manner to apply Kroneckerprecoding, the UE may determine that a total of N CSI-RS ports aredivided into K CSI-RS port groups.

Therefore, when the UE calculates, for example, a specific direction(e.g., horizontal direction) H-PMI while determining that a total of NCSI-RS ports are divided into K CSI-RS port groups, the UE may bedefined/configured to calculate the H-PMI for N/K CSI-RS ports.

Herein, the specific port group may be fixedly defined as a ‘lowest portgroup’ or ‘highest port group’ in advance.

The specific port group may be referred as the index type.

Alternatively, the specific port group may be defined as a ‘mostcentrally located port group index’.

For example, when the port group indexes are 1, 2, 3, and 4 (e.g., K=4),the ‘most centrally located port group index’ corresponds to index ‘2’or ‘3’.

As such, when the number of port group indexes is even, the ‘mostcentrally located port group index’ may be defined as a maximum integerindex (=2) which is not more than an intermediate value (e.g., 2.5 inthis case) or a minimum integer index (=3) which is more than theintermediate value.

As such, the reason for defining the specific port group as close to theintermediate value as possible is that defining the port group indexwhich is most intermediate is more excellent in overall performance ininterpolation by a Kronecker product between the H-PMI and the V-PMIthan defining/configuring the lowest port group index (since a lowermostrow is configured in an H-CSI-RS type in FIG. 27) for H-direction H-PMIcalculation as described in FIG. 27 in <Proposal content 3> to bedescribed below.

That is, the reason is that when the most intermediate port group isselected, regions to be interpolated with respect to the top and thebottom remain even to the maximum during the interpolation.

In other words, since as a distance from the corresponding port grouplocation is close as possible, there is a property in which theinterpolation is more excellently performed, a purpose is to selectupper and lower interpolation distances to be as short as possible.

As another example, when another direction (e.g., vertical direction)V-PMI is calculated, a total of K CSI-RS ports are newly configured,which are generated by choosing only the lowest (alternatively, highestor most intermediate located (the same as the above description)) portindex among N/K CSI-RS ports for each of all K port groups and a methodfor calculating the V-PMI with respect to such a configuration is alsoavailable.

Even in this case, in order to enhance the interpolation performanceupon calculating the V-PMI, it may be preferable to constitute a new CSIRS port by collecting most centrally located RS ports similarly asdescribed above.

As such, when the new CSI-RS port is constituted by collecting the mostcentrally located RS ports even in the V direction, the UE mayautomatically extract corresponding N/K H-CSI-RS ports by selecting amost centrally located row and K corresponding V-CSI-RS ports byselecting a most centrally located column at the time of beingconfigured with N port CSI-RSs and the parameter K as a whole.

Therefore, the UE performs (FD-MIMO) related CSI feedback based on themethod (e.g., Kronecker precoding) described in <Proposal content 2>,and the like.

In summary, a (unique) specific rule may be implicitlydefined/configured, through which the UE may extract N/K H-CSI-RS portsand K V-CSI-RS ports when being configured with the N port CSI-RSs andthe parameter K (K port groups).

Further, when the UE receives a new CSI-RS port configuration (e.g.,CSI-RS resource) such as 12-port or 16-port in the form of multipleaggregated CSI-RS resources from the base station, a restriction thatthe corresponding aggregated CSI-RS resources are configured not to bespaced apart from each other by X (OFDM) symbols (e.g., X=2) may bedefined/configured.

For example, when X=2, the multiple aggregated CSI-RS resources will betogether configured through two adjacent OFDM symbols like the existingCSI-RS configuration.

Accordingly, the UE does not expect that CSI-RS resources which arespaced apart from each other during a longer interval than 2 OFDMsymbols are together aggregated and not thus configured (in the specificCSI process) together.

Consequently, since the UE performs a normal operation only through sucha configuration, it may be construed that the correspondingconfiguration grants a network restriction.

As described above, when the UE does not have the network restriction,the UE needs to perform the CSI measurement between the CSI-RSs whichare spaced apart from each other by X symbols or more.

In this case, the UE may need to perform implementation such aspredicting and compensating a channel phase drift phenomenon.

Accordingly, the UE may not apply complicated implementation forpredicting and compensating the channel phase drift by granting thenetwork restriction.

That is, the implementation of the UE is continuously guaranteed onlywith respect to the CSI-RS resource received throughout the adjacent Xsymbols.

Further, in the beamformed CSI-RS based operation, and the like, anoperation that allows the UE to the best (alternatively, preferred) N(>=1) CSI-RS resource among multiple, that is, M CSI-RS resources may beconsidered.

In this case, when the CSI-RS periodicity and subframe offset among MCSI-RS resources are too largely spaced apart from each other,performance deterioration may be caused.

Accordingly, most preferably, the following restriction may be grantedso that both the CSI-RS periodicity and the subframe offset among the MCSI-RS resources are the same as each other.

In a method for supporting the beamformed CSI-RS based operation, anRel-13 CSI process configuration may include M (>1) legacy NZP (Non-ZeroPower) CSI-RS resources and each CSI-RS resource have K CSI-RS ports.

A value of K may be one of 1, 2, 4, and 8 and the K value needs to beidentical in all M NZP CSI-RS resources.

Further, all M NZP CSI-RS resources need to have the same periodicityand subframe offset.

Meanwhile, as described above, in a strict restriction that performs theCSI measurement with respect to the CSI-RS resource received throughoutthe adjacent X symbol, when when resources for transmitting M CSI-RSresources in the same subframe are insufficient, some CSI-RS resourcesmay not be allocated in the corresponding subframe.

In this case, an alleviated restriction may be granted, in a type toshow transmission of all of M CSI-RSs in specific ‘L subframes’ byalleviating a restriction related with allocation of M CSI-RS resourcesin the same subframe.

That is, when L=5, all M CSI-RS resources need to be configured to betransmitted in all of 5 (L=5).

In more detail, when the same subframe configuration restriction isgranted, information such as the CSI-RS periodicity and the subframeoffset may be commonly signaled on the signaling of the correspondingconfiguration.

In addition, in the configuration for each of M CSI-RS resources, only‘CSI-RS configuration’ information including information indicating towhich RE locations in the PRB of the corresponding CSI-RS the CSI-RS istransmitted may just be downloaded with respect to M respective CSI-RSresources.

Further, a scrambling seed (alternatively, scrambling sequence) valueapplied in sequence generation of the corresponding CSI-RS may also beindependently for each of M CSI-RS resources.

Therefore, CSI-RS resources transmitted while being overlapped with thesame RE location may be multiplexed by a sequence generated by differentscramblings.

In this case, a case where overlapped CSI-RS transmission beams areorthogonal to each other may be preferable.

Similarly, when the restriction of the type to show the transmission ofall of M CSI-RSs in the specific 1 subframes' by alleviating therestriction for M CSI-RS resources in the same subframe, that is, an‘alleviated restriction’ is granted, in the case of the information suchas the CSI-RS periodicity and the subframe offset on the signaling ofthe corresponding configuration, the periodicity and offset informationfor one specific reference CSI-RS resource (among the M CSI-RSresources) is first provided.

In addition, the periodicity and/or subframe offset information forremaining (M−1) CSI-RS resources may be configured as a relative offsetvalue compared with the transmission time of the reference CSI-RSresource.

For example, all CSI-RS periodicities may be similarly granted and inthe case of the subframe offset information, for example, one of 0, 1,L−1 values is granted for each CSI-RS to announce that the transmissiontime of the corresponding CSI-RS is shown in subframe 0, 1, . . . , orL−1 after the transmission time of the corresponding reference CSI-RSresource.

In the case of the CSI-RS periodicity when a configuration periodicityof the reference CSI-RS resource is T (ms), there may be a constraintthat the periodicity for each of remaining (M−1) CSI-RS resources may beshown only in multiples of T.

In this case, configuration information may be provided, which indicatesthat the CSI-RS resources are transmitted with a periodicity of onetime, two times, . . . , or n times of the T value as the periodicityfor each of the remaining (M−1) CSI-RS resources.

This is a type that further alleviates the restriction and an alleviatedrestriction of a type that ‘allows the transmission of all of theM-CSI-RSs to be shown at least one time in the specific L subframes’ maybe granted.

Then, the UE may be defined/configured to perform selection amongcorresponding M CSI-RS resources during an interval in which thetransmission of all M CSI-RSs is shown and report a specific(alternatively, selected) CSI-RS resource.

UE Capability (Information) Signaling

Hereinafter, a UE capability signaling method including the UEcapability information proposed in the present specification will bedescribed in detail through related embodiments.

First Embodiment

First, the first embodiment provides a method for transmitting/receivinga UE capability signaling including information on the number of allCSI-RS ports in a beamformed CSI-RS based CSI method (Class B type).

That is, the first embodiment is a method that provides the capabilityinformation of the UE regarding the number of all CSI-RS ports whichexist in the CSI process to the network through the UE capabilitysignaling.

For example, when M NZP CSI-RS resources (each CSI-RS resource includesK CSI-RS ports) are included in the CSI process, in the case whereupperlimit values for M and K values are not determined, implementationcomplexity of the UE occurs as much when the M and/or K values areconfigured as large values.

In such a case, the UE may not implement all of the numbers of all casesdue to the implementation complexity.

In the present specification, the number of NZP CSI-RS resources may beexpressed as ‘M or K’ and the number of CSI-RS ports for each CSI-RSresource may be expressed as ‘K or M’.

For example, when the number of NZP CSI-RS resources may be expressed as‘K’ and the number of CSI-RS ports for one CSI-RS resource may beexpressed as ‘M’.

The UE may transmit the UE capability signaling for the M and/or Kvalues to the base station upon initial connection with the network.

The UE capability signaling may be defined, configured, or expressed invarious forms.

For example, the UE may be defined/configured to provide to the networka capability signaling including a condition that ‘total number of ports(P=MK) in a CSI process’ depending on the configured M and/or K value isnot more than a specific P_max value.

IN this case, candidate P_max values may be pre-defined so that the UEsignals an available P_max value among specific several values.

For example, the UE may select any one of available P_max values of 8,12, 16, 24, 32, and 64 and capability-signal the selected P_max value tothe network.

In addition, the specific values such as 8, 12, 16, 24, 32, and 64 maybe predetermined.

The as 8, 12, 16, 24, 32, and 64 values are one example and anothervalue may be defined or only some values of the corresponding values maybe defined.

That is, for the UE, the total number of ports (P=MK) in one(alternatively, specific) CSI process, which is not more than the P_maxvalue may be a value directly significant to the UE complexity.

Therefore, the UE may define the P_max value in a manner tocapability-signal the P_max value.

FIG. 22 is a flowchart illustrating one example of a UE capabilityinformation signaling method proposed by the present specification.

First, the UE transmits UE capability information including firstcontrol information indicating the total number of CSI-RS portsmaximally supported by the UE to the base station using a high layersignaling (S2210).

The first control information may be referred to or expressed as totalCSI-RS port number information.

That is, the first control information is information indicating thetotal number of CSI-RS ports that the UE may support in one or aspecific CSI process.

Hereinafter, the total number of CSI-RS ports that the UE may maximallysupport is expressed as ‘P’ and P is equal to the product of the M valueand the K value (P=M*K).

Herein, the value of the first control information may be included inthe UE capability information when the beamformed CSI-RS based CSIreporting method, that is, the CSI reporting type (or class type) of theUE is ‘Class B’.

In this case, the value of the first control information may be, forexample, 8, 12, 16, 24, 32, 64, etc.

Herein, the UE capability information (or UE capability signaling) mayfurther include second control information in addition to the firstcontrol information.

The second control information is information indicating the totalnumber (M) of CSI-RS resources maximally supported by the UE in one or aspecific CSI process.

Herein, the value of the second control information may be included inthe UE capability signaling when the beamformed CSI-RS based CSIreporting method, that is, the CSI reporting type (or class type) of theUE is ‘Class B’.

Herein, the UE may transmit the first control information and the secondcontrol information together or may first transmit the first controlinformation and then transmit the second control information.

A detailed method in which the UE first transmits the second controlinformation will be described in a second embodiment to be describedbelow.

Thereafter, the base station determines a CSI-RS configuration to betransmitted to the UE based on the received UE capability signaling(S2220).

Thereafter, the UE receives the (determined) CSI-RS configurationinformation from the base station (S2230).

HereIN, the CSI-RS configuration information may be transmitted whilebeing included in a CSI process related high layer signaling.

The high layer signaling may be expressed as a CSI process informationelement (IE).

The CSI process IE may further include a CSI process ID (or Index)indicating the CSI process and CSI reporting type information for eachCSI process.

The CSI reporting type information may include at least one of thenon-precoded CSI-RS based CSI reporting type or the beamformed CSI-RSbased CSI reporting type.

The non-precoded CSI-RS-based CSI reporting type may be expressed as‘Class A’ and the beamformed CSI-RS based CSI reporting type may beexpressed as ‘Class B’.

Then, the UE receives at least one CSI-RS from the base station based onthe received CSI process related information (or CSI-RS configurationinformation) (S2240).

Herein, the at least one CSI-RS is transmitted through at least oneCSI-RS port of the base station.

Then, the UE measures a channel for the at least one CSI-RS port basedon the at least one received CSI-RS (S2250).

Thereafter, the UE reports or feeds back the channel measurement resultto the base station (S2260).

Herein, the reporting or feedback is performed every CSI process.

Second Embodiment

Next, the second embodiment provides a method for transmitting/receivingUE capability information (alternatively, signaling) includinginformation on the total number (M) of CSI-RS resources that may bemaximally supported in the beamformed CSI-RS based CSI method (Class Btype) and/or information on the total number (K) of CSI-RS portsmaximally supported for each CSI-RS resource.

As described in the first embodiment, the information on the totalnumber (M) of CSI-RS resources maximally supported by the UE isexpressed as the second control information.

Hereinafter, the information indicating the total number of CSI-RS portswhich are maximally supported in one CSI-RS resource or for each CSI-RSresource will be expressed as third control information.

That is, the second embodiment represents a method in which the UEindividually signals the M value or K value through the UE capability.

That is, the second embodiment provides a method for individually UEcapability-signaling to the base station how many NZP CSI-RS resourcesthe UE may measure in one CSI process and in this case, only up to whichvalue of the number (K) of CSI-RS ports in each NZP CSI-RS resource theUE supports or permits (in terms of implementation).

That is, the UE provides a method in which the UE individually transmitsthe M and/or K value to the base station.

Herein, the UE may transmit the capability signaling to the base stationin a manner to have a specific condition between the M value and the Kvalue.

For example, the UE may individually capability-signal the M and Kvalues in a form of K_max1 when M_max is equal to or less than aspecific value or another K_max2 when M_max is equal to or more than thespecific value.

When the base station receives a capability signaling having a specificcondition between the M and K values from the UE, the base stationprovides an associated CSI-RS configuration to the UE within a range tosatisfy corresponding capability-signaled upperlimit values at the timeof providing the CSI process and the NZP CSI-RS to the UE.

The capability signaling method of the UE, in which there is thespecific condition between the M and K values will be described in moredetail through the following embodiment.

Hereinafter, “P” represents the maximum number of supported CISprocesses which exist for each band in each band combination.

Kmax represents the (maximum) number of NZP CSI-RS resources which aresupported in one CSI process.

Nmax represents the maximum number of NZP CSI-RS ports which aresupported in one CSI process.

With respect to UE capability signaling in CSI reporting of Class Btype, the UE reports to the base station three independent values ofNmax2, Nmax3, and Nmax4 for each band combination, for each band, andfor each CSI-RS and Kmax(1,2, . . . , 8).

Nmax1(=8) represents a fixed value for K=1 configured with respect toone CSI process like the legacy.

Nmax2(=0, 8, 16) represents a value for K=2 or 3 configured with respectto one CSI process.

Nmax3(=0, 8, 16, 32) represents a value for K=4, 5, 6 or 7 configuredwith respect to one CSI process.

Nmax4(=0, 8, 16, 32, [64]) represents a value for K=8 configured withrespect to one CSI process.

Herein, Nmax=0 for given K means that it is not supported that the UE isconstituted by K CSI-RS resources with respect to the CSI process.

If P=1 for one band every band combination, the Kmax, Nmax2, Nmax3, andNmax4 are signaled only once.

If P=3 for one band every band combination, the Kmax, Nmax2, Nmax3, andNmax4 are independently signaled three times.

If P=4 for one band every band combination, the Kmax, Nmax2, Nmax3, andNmax4 are independently signaled four times.

As described above, the UE may capability-signal parameter P′ (=1, 3, or4) indicating how many CSI processes may be configured for ‘(for eachband) for each band combination or carrier aggregation’ to the basestation.

For example, when the UE reports to the base station that only P′=1 CSIprocess is supported with respect to a specific band for each bandcombination, the UE may announce at least one (alternatively, all) ofthe Kmax, Nmax2, Nmax3, and Nmax4 together with the report.

The above case represents one example in which the UE independentlyreports three Nmax values to the base station and the UE mayindependently report Nmax values of a specific number to the basestation in addition to such a method.

In this case, each Nmax value is an Nmax value when a specific K valueis assumed and capability signaling may be supported in such a manner(alternatively, a similar manner).

That is, when the UE is configured with CSI-RS resources of a specific Kvalue from the base station through CSI-RS configuration, the Nmax valuewhich represents the maximum number of CSI-RS ports supported in one CSIprocess may be defined to be capability-signaled independently for eachassumed K value.

For example, capability information of the UE indicating that Nmax forK=1 is Nmax=8, but Nmax for K=2 is supported (alternatively,implemented) up to Nmax=16 may be announced to the base station.

Therefore, when the base station configures specific K CSI-RS resourcesfor the corresponding UE, the number of CSI-RS ports in each CSI-RSresource may be appropriately configured under a condition that thetotal number of CSI-RS ports in the corresponding CSI process should notbe more than the corresponding Nmax value.

Further, the UE needs to perform capability signaling transmission insuch a manner so as to prevent a problem from occurring between the UEand the base station in transferring the corresponding information tothe base station according to the capability signaling manner.

In addition, as described above, when the base station receivescapability signaling such as ‘Nmax=16 for K=2’ from the UE, the basestation may configure 4-port CSI-RS resource 1 and 8-port CSI-RSresource with respect to 2 K (=2) CSI-RS resources, respectively.

Alternatively, the base station may configure each of 4-port CSI-RSresource 1 and 4-port CSI-RS resource 2.

Alternatively, the base station may configure each of 2-port CSI-RSresource 1 and 8-port CSI-RS resource 2.

By such a manner, the base station provides a CSI-RS configuration tothe UE so that CSI-RS ports in each CSI-RS resource are appropriatelydistributed within a range not to violate ‘Nmax=16 for K=2’ which is themaximum number of CSI-RS ports, which may be configured with respect toall configured CSI-RS resources.

As described above, ‘Nmax=0 (alternatively, N/A) (for a given K) meansthe UE does not support being configured with K CSI-RS resources for theCSI process’ means supporting an operation of the UE, which reports avalue in which Nmax=0.

For example, as a case where it is assumed that the K value is generallya large value, a case where the corresponding Nmax value is reported as‘0 (alternatively, N/A)’ may be adopted and this case may be construedas a meaning that the UE does not support the K value.

That is, the base station may not configure CSI-RS resources of K havingthe high or large value for the UE.

Further, when the UE reports that P (=3 or 4) CSI processes aresupported with respect to the specific band per band combination to thebase station through the UE capability signaling, the UE may bedefined/configured to independently capability-signal P′ parameters(e.g., capability signaling constituted by at least one of Kmax andNmax(s)) to the base station.

Therefore, when the base station intends to actually configure the P′CSI processes for the UE, the base station transmits a related CSI-RSconfiguration to the UE within a range not to be over Kmax, Nmax2,Nmax3, and Nmax4 values which may be supported for each CSI process.

Another embodiment of a capability signaling transmitting/receivingmethod including the specific condition between the M and K values willbe described.

Similarly to the above embodiment, “P” represents the maximum number ofsupported CSI processes which exist for band in each band combination,Kmax the (maximum) number of NZP CSI-RS resources supported in one CSIprocess, and Nmax represents the maximum number of NZP CSI-RS ports foreach NZP CSI-RS resource in one CSI process.

With respect to UE capability signaling in UE CSI reporting of Class Btype, the UE reports to the base station at most four independent valueswith Nmax1, Nmax2, Nmax3, and Nmax4 for each band combination, for eachband, and for each CSI-RS and Kmax(1,2, . . . , 8).

Nmax1(=2, 4, or 8) represents a fixed value for K=1 configured withrespect to one CSI process like the legacy.

Nmax2(=4, 8, or 16) represents a value for K=2 or 3 configured withrespect to one CSI process.

Nmax3(=4, 6, 16, or 32) represents a value for K=4, 5, 6 or 7 set withrespect to one CSI process.

Nmax4(=0, 8, 16, 32, or 64) represents a value for K=8 configured withrespect to one CSI process.

According to Kmax reported by the UE, the UE performs CSI-RS reportingto the base station for each band combination, each band, and eachCSI-RS.

When the UE reports Kmax=1, only one Nmax1 value is provided.

When the UE reports Kmax=2, Nmax1 and Nmax2, that is, two values areprovided.

When the UE reports Kmax=3 or 4, Nmax1, Nmax2, and Nmax3, that is, threevalues are provided.

When the UE reports Kmax=5, 6, 7, or 8, Nmax1, Nmax2, and Nmax3, andNmax4, that is, four values are provided.

The UE independently reports the capability signaling P′ times for eachband in each band combination based on (alternatively, depending on) thevalue (1, 3, or 4) of P′ reported for each band in each bandcombination.

If the UE reports P′=1 in all bands in a given band combination and thenumber of CCs is not larger than 5 in the band combination, only Nmax1=8is permitted.

Further, when P′=1 for all bands, such a constraint isdefined/configured to be granted to increase flexibility of the UEcapability signaling.

FIG. 23 is a flowchart illustrating another example of the UE capabilityinformation signaling method proposed by the present specification.

First, the UE transmits the UE capability signaling including the secondcontrol information to the base station (S2310).

The second control information is information indicating the totalnumber of CSI-RS resources that the UE may maximally support in one or aspecific CSI process.

The value of the second control information may be included in the UEcapability signaling when the beamformed CSI-RS based CSI reportingmethod, that is, the class type is ‘Class B’.

In addition, the UE capability signaling may further include the thirdcontrol information.

That is, the third control information is information indicating themaximum number of supported CSI-RS ports for each CSI-RS resource in oneor specific CSI process.

The maximum numbers of CSI-RS ports for the respective CSI-RS resourcesmay be the same as each other or different from each other.

Thereafter, the base station determines a CSI-RS configuration to betransmitted to the UE based on the received UE capability signaling(S2320).

Thereafter, the UE receives the (determined) CSI-RS configurationinformation from the base station (S2330).

As described in the first embodiment, the CSI-RS configurationinformation may be included in the CSI process IE.

Then, the UE receives at least one CSI-RS from the base station based onthe received CSI process related information (or CSI-RS configurationinformation) (S2340).

Herein, the at least one CSI-RS is transmitted through at least oneCSI-RS port of the base station.

Then, the UE measures the channel for the at least one CSI-RS port basedon the at least one received CSI-RS (S2350).

Thereafter, the UE reports or feeds back the channel measurement resultto the base station (S2360).

Herein, the reporting or feedback is performed every CSI process.

Third Embodiment

Next, the third embodiment provides a method for transmitting/receivingthe UE capability signaling including the class type information of theUE related to the CSI reporting operation.

Herein, the class type of the UE may be divided into Class A type andClass B type.

Class A type represents the UE that supports or implements thenon-precoded type CSI-RS based CSI operation and Class B type representsthe UE that supports or implements the beamformed type CSI-RS based CSIoperation.

That is, the UE transmits to the base station a capability signalingincluding UE class type information regarding whether to support anon-precoded type CSI-RS related operations (including CSI reporting)and/or whether to support a beamformed type CSI-RS related operation(including CSI reporting).

The expression of ‘A and/or B’ used in the present specification may beconstrued as ‘including at least one of A and B’.

The base station configures the CSI process and NZP CSI-RS resource(whether it is a non-precoded type or a beamformed type) and/or CSIreporting related configurations of the UE, which are associated withthe configuration for the UE based on the capability signaling includingthe UE class type information and provides the configurations to the UE.

In addition, the UE may individually provide to the base stationinformation indicating whether a hybrid scheme utilizing both thenon-precoded CSI-RS based CSI method and the beamformed CSI-RS based CSImethod is supported, through the capability signaling.

Fourth Embodiment

Next, the fourth embodiment provides a method in which the UE transmitsto the base station a UE capability signaling indicating whether tosupport only specific some parameters (alternatively, schemes) among(non-precoded CSI-RS based or class A type) CSI reporting operationrelated parameters (alternatively, schemes).

For example, there may be a configurable codebook scheme shown in Table10 below among non-precoded CSI-RS based CSI reporting related schemes.

In the fourth embodiment, a case of rank 1 will be described as oneexample.

TABLE 10 (When a KP structure is adopted, a rank-1 precoder W_(m,n,p)has the following form in a master codebook.)${W_{m,n,p} = {\begin{bmatrix}w_{0} & w_{1} & \ldots & w_{N_{CSIRS} - 1}\end{bmatrix}^{t} = {\frac{1}{\sqrt{N_{CIRS}}}\begin{bmatrix}{v_{m} \otimes u_{n}} \\{\varphi_{p}\left( {v_{m} \otimes u_{n}} \right)}\end{bmatrix}}}},$ herein, NC_(SIRS) = number of configured CSI-RS portsin the CSI-RS resource (the number of CSI-RS ports configured in theCSI-RS resource), e.g., 12, 16, etc. u_(n) is a N × 1 oversampled DFTvector for a first dimension, whose oversampling factor is o₁. v_(m) isa M × 1 oversampled DFT vector for a second dimension, whoseoversampling factor is o₂.${\varphi_{p}\mspace{14mu}{is}{\mspace{11mu}\;}a\mspace{14mu}{co}\text{-}{phase}},{e.g.},{{in}\mspace{14mu} a\mspace{14mu}{form}\mspace{14mu}{of}\mspace{14mu} e^{\frac{2\;{\pi p}}{4}}},{p = 0},1,2,3.$When a dual codebook structure is also adopted as well as the KPstructure, precoder indexes m, n, and p are indicated by PMIs ofi_(1,1), i_(1,2), and i₂ and herein, i_(1,1) and i_(1,2) correspond tofirst PMI(W1) and, i₂ 

 ; corresponds to second PMI(W2). i_(1,1) determines the beam group inthe first dimension; i_(1,2) determines the beam group in the firstdimension; and i₂ selects one beam among the beams of the beam groupconstituted by {i_(1,1), i_(1,2)} and determines co-phase. Effectively,i₂ may be de-composed to i_(2,1), i_(2,2), p in order to indicate thebeam selection and co-phase. With respect to the master codebookstructure depending on the structure proposed in the presentspecification, the following parameter group needs to be embodied foreach dimension d. an oversampling factor o_(d); a beam skip number s_(d)(for W_(1,d); the first beam in adjacent beam group is s_(d) beams awayfrom that of the current beam(W_(1,d).); a beam spacing number p_(d)(for W_(2,d); the beam spacing within the beam group is p_(d)) and; anumber of beams L_(d) (number of beams in a beam group in dimension d)In order to support various antenna deployment scenarios and antennaconfigurations, some parameters among the above parameters need to beconfigured.

As an advantage of the configurable codebook structure shown in Table10, various parameters in Table 10 are configured for and provided tothe UE through higher layer signaling to perform the CSI reportingoperation by applying a codebook generated with the correspondingparameters.

Accordingly, a codebook suitable for various deployment scenarios andantenna configurations are optimized even with respect to variousdeployment scenarios and antenna configurations through thecorresponding configurable codebook structure to be applied to the UE.

Therefore, it is advantageous in that system performance may beoptimized through the configurable codebook structure shown in Table 10.

However, in terms of the implementation of the UE, there may be adisadvantage in that the implementation complexity may increase becausethe UE needs to implement codebooks which may be generated with respectto all combinations of candidate values which the parameters may have asthe parameters may be arbitrarily configured.

Accordingly, hereinafter, in order to reduce or solve the implementationcomplexity of the UE, there is provided a method in which the UEtransmits the UE capability signaling including information indicatingonly which value(s) of the respective parameters may be applied to theUE to the base station.

For example, the UE may capability-signal a list of specific valueswhich are implemented (alternatively, applicable) thereby to the basestation with respect to at least one of parameters 1) to 4) given below.

Herein, the UE may capability-signal a separate value for each dimensionwith respect to at least one of parameters 1) to 4) given below.

1) an oversampling factor o_(d).

2) a beam skip number s_(d): The first beam in adjacent beam group iss_(d) beams away from that of the current beam with respect to W_(1,d).

3) a beam spacing number p_(d)): For W_(2,d); the beam spacing withinthe beam group is p_(d).

4) a number of beams L_(d): represents the number of beams in a beamgroup in dimension d.

With respect to the respective parameters 1) to 4), the UE maycapability-signal some values among, for example, 1, 2, 4, 8, 16, . . .values to the base station.

Alternatively, the UE may capability-signal a maximum value and/or aminimum value among the values of 1, 2, 4, 8, 16, . . . to the basestation.

As described above, the UE may transfer individual respective parametersto the base station through the capability signaling.

However, as another example, a parameter set shown by a specificcombination of some parameters among the parameters 1) to 4) may benewly defined.

At least one of the newly defined parameter set (information) may becapability-signaled to the base station.

One example of the new parameter set defined by combining theparameters 1) to 4) may be given below.

(e.g.,) parameter set 1 may be constituted or defined like {o_(d-1)=8,o_(d-2)=16, s_(d-1)=2, s_(d=2)=2, p_(d=1)=1, p_(d=2)=1, L_(d=1)=4,L_(d=2)=4}.

Like the above example, another parameter sets 2, 3, . . . may beconstituted by a combination of some of the parameters 1) to 4).

Accordingly, the UE may capability-signal at least one parameter setdefined as above to the base station.

In this case, when the base station provides the configurable codebooktype configuration information to the UE, the base station selects atleast any one of the parameter sets included in the capability signalingtransmitted by the UE and configures and provides the selected parameterset for and to the UE.

Additionally, in capability-signaling of the individual parameters orthe parameter set form, the codebook parameters and the codebookparameter set may be configured, which vary depending on the number ofCSI-RS ports of a specific NZP CSI-RS resource to which thecorresponding codebook is to be applied.

Accordingly, the UE may be defined/configured to capability-signal theparameter set information configured as the parameters 1) to 4) or thecombination of the parameters 1) to 4) for each (CSI-)RS port numberconsidered in the capability signaling to the base station (that is, thenumber of CSI-RS ports in the corresponding resource per NZP CSI-RSresource, which is considered).

The number of cases of ‘the number of (CSI-)RS ports’ considered abovemay be defined by transmitting to the base station the parameter or theparameter set related capability information by the UE with respect tois the total number of CSI-RS ports per specific CSI process supported(in a specific TM) or the number of CSI-RS ports in a specific NZPCSI-RS resource.

Alternatively, the base station may announce whether the UE provides theparameter or parameter set-related capability signaling information withrespect to a specific ‘(CSI-) RS port number’ value as part of thesystem information at initial connection with the UE.

In more detail, a separate CSI reporting class identified as the type ofCSI reporting Class A and Class B in the CSI process configuration maybe configured/identified.

That is, the UE receives from the base station the CSI processconfiguration information of a type in which the CSI reporting type orthe CSI reporting related class is configured from the base station.

Thereafter, the UE verifies whether Class A or Class B is configured inrelation with the CSI reporting based on the received CSI processconfiguration information.

Thereafter, the UE performs the CSI reporting operation associated withthe verified class based on the verification result.

Accordingly, in terms of the UE capability signaling, when the basestation receives information related with Class (type) of the UE fromthe UE, the base station may know whether all association operations(e.g., CSI measurement, CSI reporting, and the like) depending on ClassA type and/or Class B type may be performed (alternatively, implemented)or whether only an association operation (e.g., CSI measurement, CSIreporting, etc.) depending on one specific class type among two classtypes may be performed, or whether all of the operations of Class A andClass B are not supported, through the capability signaling of the UE.

In addition, the UE may individually independently capability-signal tothe base station the associated parameters (e.g., the number of CSI-RSports) that may be supported for Class A (type) and the associatedparameters (e.g., the total number of CSI-RS ports, the number of CSI-RSresources, the maximum number (K) of supported CSI-RS resources, thenumber (N_k) of CSI-RS ports per CSI-RS resource, L value for L-port CSIreporting and associated parameters) which may be supported in Class B.

That is, the UE may independently capability-signal each of theassociated parameters for supporting Class A and/or the associatedparameters for supporting Class B to the base station.

Herein, the associated parameters for supporting Class A may be codebookparameters including information including N1 (the number of horizontalantenna ports), N2 (the number of vertical antenna ports), O1 (ahorizontal oversampling value), O2 (a vertical oversampling value),codebook config., and information indicating whether CDM−4 is supportedor a new parameter set configured by the combination of some parametersof the codebook parameters.

As one example, the associated parameters for supporting Class A mayinclude codebook configuration information related with a 2D codebook.

The codebook configuration information may include codebookconfiguration information for selection of the beam group non-precodedCSI-RS (alternatively, Class A type), that is, codebook config. (index)1, 2, 3, and 4.

The codebook configuration information may be configured differentlyaccording to the rank.

Accordingly, the base station provides to the UE the CSI configurationso as not to violate the capability signaling information of the UE,which is associated with the corresponding class type according to whichclass of Class A and Class B is configured.

Further, at least one of information included in the capabilitysignaling proposed in the present specification may be signaledindividually/independently 1) for each specific band (e.g., componentcarrier; CC), 2) for specific band combination (when the CA isconsidered, a carrier aggregation combination), or 3) for each bandcombination.

In the case of Term 1), there is an advantage in that even though the CAis considered, detailed capability information may be more flexiblytransferred for each band (e.g., CC).

Tem 2) may be defined/configured when the capability signalingapplicable for each specific considered band combination is transferredand a CA related configuration depending on the corresponding bandcombination (alternatively, CA) is thus provided (e.g., Pcell/Scelladdition configuration, etc.), when the CSI process associatedconfiguration is provided (through the CSI process IE) for each CC, whenthe capability signaling is transferred in a form in which theinformation included in the capability signaling is commonly applied tothe corresponding band combination (alternatively, for eachcorresponding band combination when the capability signaling istransferred independently for each band combination).

FIG. 24 is a flowchart illustrating yet another example of the UEcapability information signaling method proposed by the presentspecification.

First, the UE transmits the UE capability signaling including fourthcontrol information to the base station (S2410).

The fourth control information may be simply expressed as controlinformation.

The fourth control information is information indicating which codebookconfiguration a UE related to the 2D-AAS structure supports (orimplements).

The fourth control information indicates a codebook configurationrelated with Class A, that is, the non-precoded CSI-RS operation.

Further, the fourth control information may indicate a codebookconfiguration related to beam group selection for long-term CSI feedbackin the 2D-AAS structure.

The codebook configuration may include at least one of codebookconfigurations 1 to 4.

That is, the UE may announce which codebook configuration of codebookconfigurations 1 to 4 related with the 2D-AAS structure is supported orwhich codebook configuration is implemented to base station through thecapability signaling.

The codebook configuration may vary depending on the rank number.

Thereafter, the base station determines a codebook configuration to betransmitted to the UE based on the received UE capability signaling(S2420).

Therefore, the UE receives the higher layer signaling including the(determined) codebook configuration from the base station (S2430).

Thereafter, the UE receives the CSI-RS or at least one CSI-RS porttransmitted through at least one antenna port from the base stationbased on the received higher layer signaling (S2440).

In detail, the UE may select a beam (alternatively, antenna port) groupfor receiving at least one CSI-RS based on the determined codebookconfiguration.

In addition, the UE receives and measures the CSI-RS through at leastone beam in the selected beam group.

Thereafter, the UE estimates the channel through the received CSI-RS(S2450).

Thereafter, the UE determines a precoding matrix related with theestimated channel in the codebook (S2460).

Therefore, the UE feeds back a precoding matrix index (PMI)corresponding to the determined precoding matrix to the base station(S2470).

Herein, the feedback for the selected beam group is performed during thelonger term and the feedback for the beam in the selected beam group isperformed during the short term.

That is, the feedback is divided into long-term feedback and short-termfeedback.

Herein, the reporting or feedback is performed every CSI process.

<Proposal Content 1-1: New CSI-RS Resource Configuration>

Next, a method for configuring a new CSI-RS resource will be described.

In the above description, a focus is brought to specific cases of12-port and 16-port CSI-RS patterns.

However, when it is considered that the port will be extended up to 32ports or more in the future, it may be more advantageous to maintainslight flexibility in configuring M (>8)-port CSI-RS resource in a morenormal form.

In such a viewpoint, <Proposal content 1-1> to be described belowconsiders new CSI-RS resources that may be configured with multipleCSI-RS resources in legacy 2-port, 4-port, and/or 8-port.

According to <Proposal content 1-1>, a specific M-port CSI-RS may besupported, in which candidate M values may be restricted to a multiple4, that is, M=4, 8, 12, 16, etc. for simplification.

<Proposal content 1-1> may be divided into two methods as below.

(Method 1): For the UE that supports EBF/FD-MIMO, the CSI process may beconfigured with multiple legacy (4-port) CSI-RS resources.

(Method 2): For the UE that supports EBF/FD-MIMO, a new type of CSI-RSresource may be configured to include multiple merged legacy (4-port)CSI-RS resources.

Further, for CSI-RS enhancements that support 8 CSI-RS ports or more(e.g., 16, 32, 64, etc.), multiple different beamformed CSI-RSport-groups may be configured per CSI-RS configuration

In addition, different CSI-RS port-groups may be transmitted indifferent subframes.

Consequently, a considerable number of CSI-RS ports among all CSI-RSports may be TDXed in a subframe level while satisfying the maximum 6 dBCSI-RS power boosting condition at present.

Potential Codebook and CSI Feedback Enhancements

Hereinafter, for easy description, it is assumed that the UE isconfigured with a total of 32 CSI-RS ports in order to support FD-MIMOCSI feedback.

For example, the UE may have four port-groups and recognize that eachport group is associated with the existing 8-port CSI-RS pattern asillustrated in FIG. 25 below.

The network allows four different vertical beamformed CSI-RSs to betransmitted per cell.

In this case, the respective beamformed CSI-RSs correspond to differentport groups.

Each UE connected to the corresponding cell may perform the FD-MIMO CSIfeedback and include the following two parts for a CSI feedback chain.

Part 1: port-group feedback selected based on selection of thecorresponding codebook

Part 2: horizontal short-term CSI feedback based on existingconstant-modulus

The periodicity of the vertical beam selection feedback of Part 1 may berelatively longer than that of the existing horizontal feedback, thatis, the feedback of Part 2.

In respect to RI and PMI feedback, whether the UE is permitted to selectone or more port groups needs to be first examined.

When a situation for a normal structure is assumed, the UE calculates anFD-MIMO association precoder (W_(D)) by Equation 20 below and reportsthe calculated FD-MIMO association precoder to the base station.W _(D) =└w ₀ ^((V)) ⊗W ₀ ^((H)) w ₁ ^((V)) ⊗W ₁ ^((H)) Λw _(R) _(V) ⁻¹^((V)) ⊗W _(R) _(V) ⁻¹ ^((H))┘,[Equation20]Herein, W _(D) ^((V))=[w ₀ ^((V)) w ₁ ^((V)) Λw _(R) _(V) ⁻¹ ^((V))].

Herein, W_(D) ^((V)) is selected by codebook selection and W_(D) ^((H))is selected by the existing constant-modulus codebook.

R_(V) represents the rank of W_(D) ^((V)) and represents how many portgroups are selected by the UE.

w_(r) ^((V)) is a selection vector and represents a selected r-th portgroup.

W_(r) ^((H)) corresponds to the existing horizontal precoding matrixonly in the r-th selected port group.

When the rank of W_(r) ^((H)) is expressed as R_(H)(r), all ranks of theFD-MIMO association precoder W_(D) are given by

$\sum\limits_{r = 0}^{R_{V} - 1}{{R_{H}(r)}.}$

Therefore, all ranks are the sum of respective horizontal ranks R_(H)(r)obtained every selected port group r.

FIG. 25 illustrates one example of an 8-port CSI-RS pattern in anexisting PRB pair.

Hereinafter, an evaluation result for a comparison between the long termvertical feedback and the dynamic vertical feedback having the existinghorizontal feedback may be verified.

A long-term vertical feedback case may be regarded as baseline category2 having virtual sectorization.

In addition, a dynamic vertical feedback case as a special case isrelated with a proposed method having a restriction of vertical rank 1.

As illustrated in FIG. 26, when all 32 antenna elements for 2D-AAS areconsidered, mapping transceiving Units (TXRUs) and the antenna elementsone to one is assumed.

FIG. 26 is a diagram illustrating one example of a 2D-AAS antennaconfiguration.

Table 11 given below is a table showing a simulation result of comparinglonger-term and short-term based on the vertical feedback.

A vertical beam selection margin of 3 dB is applied to the long-termvertical feedback.

TABLE 11 UE average 5% UE Throughput throughput (kbps) (kbps) Long-termvertical feedback 2779(100%) 509(100%) Dynamic vertical feedback2927(111%) 596(117%)

As shown in Table 11, it can be seen that the performance of the dynamicvertical feedback case is a little better than the long-term verticalfeedback case in 5% UE throughput.

It is anticipated that a vertical channel variance is small.

Accordingly, dynamic channel adaptation does not seem to be so effectivein this case.

However, in an environment having a larger vertical channel variance,such as an HetNet environment, in a case where there is no vertical rankrestriction in which R_(V) may become 1 or more, or in an environmenthaving 2 UE Rx antenna cases or more, the dynamic channel adaptationneeds to be further researched.

Hereinafter, contents related with a CSI process definition to which themethods proposed in the present specification may be applied will bedescribed.

(Concept 1)

Concept 1 is the CSI process for PMI based reporting and there are twoclass types (class A type and class B type) in the CSI reporting.

The CSI reporting CSI process having the PMI may be configured to haveany one of two CSI reporting classes (class A and class B) or both twoclasses.

Class A: The UE reports the CSI to the base station according to W=W1*W2codebook based on {[8], 12, 16} CSI-RS ports.

Class B: The UE reports an L port CSI to the base station by assumingany one of four methods given below.

Method 1) Beam selection indicator (BI) for selecting the beam andL-port CQI/PMI/RI for the selected beam

In the CSI process, the total number of ports configured with respect toall CSI-RS resources is larger than L.

Method 2) L-port precoder from a codebook reflecting both co-phasing byassociating the beam selection and two crossing polarizations

The total number of ports configured in the CSI process is L.

Method 3) A codebook reflecting the beam selection and the L-port CSIfor the selected beam

In the CSI process, the total number of ports configured with respect toall CSI-RS resources is larger than L.

Method 4) L-port CQI/PMI/RI

The total number of ports configured in the CSI process is L.

When the CSI measurement restriction is supported, Method 4 iscontinuously configured.

(Concept 2)

CSI process (relationship with the CSI-RS resource) having CSI reportingClass A and Class B

The CSI process is associated with K CSI-RS resources/configurationshaving N_(k) ports for a k (k>=1)-th CSI-RS resource.

The maximum total number of CSI-RS ports in one CSI process

The maximum total number of CSI-RS ports is 16 with respect to CSIreporting class A.

12-port/16-ports CSI-RS is an aggregation of K (K>1) CSI-RSresources/configurations having 2/4/8 ports.

<Proposal Content 1-2>

A bitwidth of the beam selection indicator (BI) which the UE reports tothe base station depends on a configured K value and has a maximum of 3bits.

Value of N_(total)

The value of N_(total) indicating the total number of CSI-RS portsconfigured in the Rel-13 CSI process varies depending on the UEcapability.

For example, when it is considered that an integer multiple of thenumber of ports (1, 2, 4, or 8 ports) which EBF/FD-MIMO maylegacy-configure with respect to class B and 12-port and 16-port CSI-RSsfor class A are newly supported, an available N_(total) value may become{12, 16, 24, 32, 48, 64}.

For example, the N_(total) value may be fixed to one specific value suchas 32 or 64, but one commonly permitted N_(total) value may not bepreferable. The reason is that when the N_(total) value has one specificvalue, the UE implementation and complexity may be significantlyinfluenced.

It is advantageous to have slight flexibility in term of the UEimplementation for targeting a high-capability UE or low-capability UE.

In addition, defining candidate N_(total) values may be preferred interms of flexibility.

Accordingly, the N_(total) value depends on the UE capability forpermitting flexible UE implementation that targets different situations.

For example, as the N_(total) value, the candidate values such as 12,16, 24, 32, 48, and 64 may be preferably defined.

Hereinafter, CSI reporting features of Class A and/or Class B will bedescribed in brief.

First, the UE may capability-signal UE capability information indicatingwhether to support Class A and/or Class B CSI reporting to the basestation.

The reason is that Class A and Class B perform different CSI reportingrelated operations.

Accordingly, it is more advantageous to have the flexibility in terms ofthe implementation of the UE for selectively implementing any one classof Class A and Class B or both Class A and Class B.

Therefore, the base station configures only the class in the CSI processconfiguration which the UE capability-signals for the UE.

Further, the UE capability-signals to the base station N1, N2, O1, O2,Codebook Config. (e.g., codebook config., Indexes 1, 2, 3, and 4), andinformation indicating whether CDM-4 is supported, that is, the codebookparameters related with class A, or information obtained by associatingsome parameters among the codebook parameters to report more detailedparameters for each class to the base station.

With respect to Class B, the UE may report whether to support only W2feedback having PMI−config=1 to the base station and when K>1, the Kvalue maximally supported by the UE may be announced to the basestation.

Further, the UE may transmit the number of additional supported UpPTSsymbols, the number of supported combs, and information indicatingwhether an Rel-13 DMRS table is supported to the base station throughthe capability signaling.

Further, the UE may transmit a capability signaling includinginformation indicating whether to support (alternatively, implement)only enhanced periodic SRS transmission, or whether to support(alternatively, implement) only enhanced aperiodic SRS transmission, orwhether to support both the enhanced periodic SRS transmission and theenhanced aperiodic SRS transmission in association with an RRCconfiguration message for enhanced periodic SRS/aperiodic SRStransmission to the base station as shown in Table 12 below.

Therefore, the base station may configure the UE to perform additionalSRS transmission based on the capability signaling transmitted by thecorresponding UE.

TABLE 12 Sounding RS-UL-Config Dedicated-extended Sounding RS-UL-ConfigDedicated-Aperiodic UpPTs extended UpPTs SRS configuration parameter forextended SRS configuration parameter for extended UpPTS for trigger type0 UpPTS for trigger type 1 Same set of parameters and value ranges areSame set of parameters and value ranges are used as in SoundingRS-UL-ConfigDedicated, used as in Sounding RS-UL- with an exception ofadding new ConfigDedicatedAperiodic-r10, with anparameter(number-of-combs) and revising exception of adding newparameter(number-of- value ranges of the parameters combs) and revisingvalue ranges of the (transmissionComb, cyclicShift) parameters(transmissionCombAp, cyclicShiftAp) Independently configured per cellIndependently configured per cell This parameter is configured only whenThis parameter is configured only when Number-of-additional-Uppts isconfigured. Number-of-additional-Uppts is configured.

Further, the UE may transmit a capability signaling includinginformation indicating whether to support (alternatively, implement)only a channel MR operation, or whether to support (alternatively,implement) only an interference MR operation, or whether to support boththe channel MR operation and the interference MR operation inassociation with an RRC configuration message for channel measurementrestriction (MR) and/or interference MR to the base station as shown inTable 13 below.

Therefore, the base station configures the channel MR and/orinterference MR for the UE based on the capability signaling transmittedby the corresponding UE.

TABLE 13 Channel-Measurement-RestrictionInterference-Measurement-Restriction Indicate whether measurementrestriction is on Indicate whether measurement restriction is on or offfor channel measurement or off for interference measurement 1 bit toindicate whether measurement 1 bit to indicate whether measurementrestriction is on or off for channel restriction is on or off forinterference measurement measurement Independently configured per CSIprocess per Independently configured per CSI IM per CSI subframe subsetper cell process per subframe subset per cell Applies for class B 1 = ON1 = ON 0 = OFF 0 = OFF

Fifth Embodiment

A new CSI process supports only PUSCH based aperiodic CSI reporting(PUSCH based aperiodic CSI reporting).

In addition, in the case of PUCCH-based CSI reporting, one legacy CSI-RSresource corresponding thereto is added and inserted at all times,thereby performing only legacy PUCCH-based periodic CSI-RS reporting.

In this case, the new CSI process may configure pairing of one new(e.g., 12 or 16 port) CSI-RS resource and one legacy (e.g., 1, 2, 4, or8 port) CSI-RS resource.

In addition, the new CSI process divides or separates a new CSI-RSresource to perform aperiodic CSI reporting and the legacy CSI-RSresource to perform legacy CSI-RS resource.

However, limiting the PUCCH-based periodic CSI reporting to only applyto legacy CSI-RS resources in the new CSI process may have a problem ofimpairing or limiting the efficiency and effectiveness of periodicCSI-RS feedback.

Accordingly, a fifth embodiment to be described below provides a methodfor performing PUCCH-based periodic CSI reporting on a new CSI-RSresource in a new CSI process.

When the PUCCH-based periodic CSI reporting is performed using thelegacy CSI-RS resource, a legacy CSI process is used.

That is, there is provided a more effective method of operating CSIreporting that prevents UE capability from being not greater.

For example, from the viewpoint of capability signaling, the UE maytransmit to the base station capability signaling related to legacy (P:number of supported CSI processes) P value (e.g., 1, 3, 4) for each bandcombination (for each CA).

Herein, as additional capability signaling of the UE, the UE may notifyto base station information indicating how many CSI processes in whichenhanced Class A such as 16-port or 12-port is supported may be furtheradded.

For example, it is assumed that when the UE transmits to the basestation capability signaling including the number of legacy Ps, a valueof ‘P=3’, the UE transmits to the base station capability signalingincluding the number Q of additional CSI processes, a value of ‘Q=2’(for example, in the case of 16-port).

In this case, the base station may recognize that the UE may configureor support a total of P+Q=5 CSI processes.

At this time, it is possible to restrict that only aperiodic (A)-CSIreporting may be configured for ‘Q=2’, that is, the added CSI process.

Further, for ‘P=3’, periodic (P)-CSI/aperiodic (A)-CSI are all possible,and as described above, for ‘Q=2’, only A-CSI reporting may beconfigured.

As a result, a restriction that a new CSI process should always includeall two CSI-RS resources may be avoided.

In addition, the UE may transmit capability signaling to the basestation, which includes an additional parameter N ‘for each bandcombination per band’ and/or ‘for each band combination’.

In the content related with the calculation relaxation of the currentlydefined CSI calculation complexity, if the triggering is performedwithin X (e.g., X=4 ms) for P+Q unconditionally, an operation that allA-CSI reportings may be performed may be modified.

Accordingly, the UE may be defined to perform A-CSI reporting only up toN corresponding to the additional parameters.

For example, P+Q=5, but N=3.

Two legacy configurations of P=3 may be implicitly considered as a pairrelationship only for PUCCH based reporting mode (which is a kind of Q=2enhanced configuration).

In addition, there is an advantage that P+Q=5, but the number ofsimultaneous A-CSI reportings may be still maintained by P=N=3 to be thesame as that of the legacy.

<Proposal Content 2>

When a non-precoded CSI-RS method is considered for supporting a FD-MIMOoperation, the number of NZP CSI-RS ports settable per CSI process needsto be increased.

Potential non-precoded CSI-RS enhancements

For a beamformed CSI-RS, a TDM type design for different CSI-RSport-groups needs to be considered.

Each CSI-RS port group includes different beamformed CSI-RS ports.

Herein, the scale of a TDM may be several subframes or more.

Due to the application of different vertical-beamformed ports for oneport-group, different port-groups need not be transmitted at the sametime (or almost simultaneously, for example, within a pair of OFDMsymbols).

A CSI feedback of the UE may include a port-group selection feedbackbased on the codebook selection, like a vertical feedback, and includean existing short-term CSI feedback based on an existingconstant-modulus (CM) codebook like a horizontal feedback.

In the case of considering a design for a non-precoded CSI-RS basedmethod with 8 ports or more (e.g., 16, 32, or 64 ports), asubframe-level TDM between CSI-RS ports within the same CSI-RS resourceneeds to be measured at all non-precoded CSI-RS ports.

The non-precoded CSI-RS design method may be classified into thefollowing two methods (a TDM-based non-precoded CSI-RS and an FDM-basednon-precoded CSI-RS).

Scheme 1: Design of TDM-based non-precoded CSI-RS

FIG. 25 shows the existing 8-port CSI-RS patterns, and it can be seenthat a total of 40 ports per PRB pair for each subframe may be used.

According to the same design principle in terms of time spread, RS portswithin one CSI-RS resource may be defined to support FD-MIMO of amaximum of 24 ports (all REs in the ninth and tenth OFDM symbols in FIG.25) for each CSI-RS resource.

However, a direct extension for increasing the number of CSI-RS ports to24 may still not cover a case for 32 ports and 64 ports.

Further, the 24-port CSI-RS may be used only once per subframe, andother 8-port CSI-RS pattern 0 (in the fifth and sixth symbols in FIG.25) and 8-port CSI-RS pattern 4 (in the twelfth and thirteenth symbolsin FIG. 25) may not be used to support the FD-MIMO.

The 8-port CSI-RS patterns present in the PRB pair will be describedwith reference to FIG. 25 above.

Particularly, in FIG. 25, accurate 32-port CSI-RS configurationincluding 8-port CSI-RS patterns 1, 2, 3, and 4 may be defined.

Herein, the time spread of the RS port is a length of 4 OFDM symbols.

In this case, the remaining 8-port CSI-RS pattern 0 may be used forlegacy UE support.

Similarly, accurate 16-port CSI-RS configuration including 8-port CSI-RSpatterns x and y may be defined.

Herein, (x,y) may be (1,2), (1,3), or (2,3).

In this case, the time spread of the RS port has the same OFDM symbollength as the legacy.

Alternatively, in order to design a 16-port CSI-RS configuration, it mayalso be considered that the 8-port CSI-RS pattern 4 is included.

(Proposal 1): A non-precoded CSI-RS configuration to 32 ports in onesubframe may be considered by reusing legacy 8-port CSI-RS patterns.

To support a 64-port CSI-RS configuration for FD-MIMO, a non-precodedCSI-RS design for TDM may include two schemes as follows.

Each scheme has extension of multiple subframes and additional RE usage,as summarized below.

(Method 1-1): Additional extension in multiple subframes

(Method 1-2): Use additional REs in addition to existing candidateCSI-RS REs

First, scheme 1-1 allows the merging of multiple subframes for REsavailable for 64 or more CSI-RS ports.

However, in this case, a part for overcoming a channel phase offsetbetween RS ports transmitted in subframes of different types ofcompensation methods is required.

For example, the UE may compensate for the channel phase offsetevaluated by the CRS measured in different subframes.

Accordingly, the above contents are applied to measure the CSI-RS-basedchannel when acquiring the CSI for FD-MIMO.

Next, method 1-2 defines additional REs that may be used for CSI-RSports for the FD-MIMO purpose.

For example, the same patterns of the existing 8-port CSI-RS patterns 1,2, and 3, for example, new pattern indexes of patterns 1 a, 2 a and 3 amay be repeated the second and third OFDM symbols.

Accordingly, for supporting the FD-MIMO, a total of 8 8-port CSI-RSpatterns may be included in one subframe, resulting in 64 ports.

For such a configuration, the PDCCH length is limited to the first twoOFDM symbols.

The occurrence of such a specific subframe may be preset to the UE orprovided to the UE through (higher layer) signaling.

(Proposal 2): In addition to the existing candidate CSI-RS REs,additional REs may be considered to support the 64-port CSI-RSconfiguration in one subframe.

(Method 2): Design of FDM-based non-precoded CSI-RS

The approach of the FDM-based non-precoded CSI-RS design may firstconsider an RB level FDM CSI-RS port to increase the total number ofCSI-RS ports configured to the UE for supporting FD-MIMO.

As shown in FIG. 25, in the currently available CSI-RS patterns, thesame RS port is allocated to every 12 subcarriers, and the RS densityfor one CSI-RS port is ‘1’ for each PRB pair.

In the case of defining a new CSI-RS pattern with RBs proposed in scheme2, for example, assuming that the same RS port is allocated to every 24subcarriers, only existing CSI-RS patterns are reused to support up to64 port CSI-RS configuration in one subframe.

Potential Codebook and CSI Feedback Enhancements

The UE may be configured to have 8 non-precoded CSI-RS ports or more perCSI process to support FD-MIMO.

For example, the UE may acquire a CSI-RS by using a predefined codebookwhile measuring full CSI-RS ports such as 16, 32, and 64 ports.

Further, the codebook used in such a situation may be a full-sizedcodebook such as a 16-tx, 32-tx, or 64-tx codebook that needs to benewly defined.

However, designing such a new codebook generally requires much effort.

Accordingly, it is natural to have a systematic codebook structure basedon a Kronecker product between existing or DFT-based constant modulus(CM) codebooks.

In the method of Kronecker precoding, a full channel precoding matrix Pmay be acquired by the following Equation 21 through V-precoding P_(V)and H-precoding P_(H) with Kronecker product operators.P=P _(V) ⊗P _(H)  [Equation 21]

Herein, a horizontal domain codebook for acquiring H-precoding P_(H) maybe an existing LTE codebook such as 2-tx, 4-tx, and 8-tx codebooks.

However, a type of codebook for a vertical domain codebook preferablyuses the same LTE codebook, DFT codebook, or the like for FD-MIMOsupport.

In the case of using options to be listed below for each verticalcodebook, a performance difference will be described.

Option 1: 2-bit DFT codebook

Option 2: 3-bit DFT codebook

Option 3: Rel-8 4-Tx codebook

For evaluation for each option, it is assumed that non-co-channel HetNetscenarios for a macro cell (8, 4, 2, 8) and a small cell (4, 2, 2, 16)are considered.

For the macro cell, 1 TXR per polarization is assumed, and for the smallcell, 4 TXR per polarization is assumed.

In addition, a bias value for cell association between the small celland the macro cell is 1.8 dB.

With respect to Option 1, a {75.5, 90.0, 104.5, 120.0} etilt is used forthe DFT codebook.

Further, with respect to Option 2, a {41.4, 60, 75.5, 90, 104.5, 120,138.6, 180} etilt is used for the DFT codebook.

Further, with respect to Option 3, (Re1.8) 4-Tx codebook is used forsimulation.

An evaluation result of a full buffer model for each option 1, 2, or 3is illustrated in Table 14 below.

That is, Table 14 illustrates the results of a full buffer simulationfor 5%, 50% UE and average sectors according to different verticalcodebook options.

TABLE 14 Average sector 5% UE 50% UE Throughput Throughput Throughput(bps/Hz) (bps/Hz) (bps/Hz) Option 1 2.56 0.138 (99%) 0.486 Option 2 2.620.139 (100%) 0.499 Option 3 2.62 0.141 (101.1%) 0.500

Referring to Table 14, performance of each of options 1, 2 and 3 may bealmost the same as each other.

In terms of the performance, sufficient performance may be acquired onlyby using 4 vertical codewords such as Option 1.

That is, when considering the performance viewpoint for the verticalcodebook, it can be seen that it is sufficient to use a 2-bit DFTcodebook.

<Proposal Content 3>

Hereinafter, when a large number of transmission antennas areimplemented in the base station for the FD-MIMO operation, whether theUE measures how many CSI-RS ports will be described.

When considering FD-MIMO in a 2D antenna array system with a largenumber of antennas, it is necessary to consider whether N-port (N>8)CSI-RS configuration is required.

In a massive MIMO system having a large number of antenna elements, thenumber of CSI-RS transmission ports may increases proportionally as thenumber of antenna elements increases.

Even though direct extension may be considered so that the number ofCSI-RS ports can be set to 8 or more (for example, extending locationsof candidate REs per PRB pair), this may have a significant effect on acurrent specification including modification of the CSI-RS configurationwith N>8 ports and a location of the corresponding RE or subframe-levelextension for covering a large number of N-port CSI-RS configurations.

In addition, as the number of Ns per CSI-RS configuration increases, theRS resource overhead also increases proportionally and as a result,throughput may be reduced.

(Proposal 1): Need to review whether N-port (N>8) CSI-RS configurationneeds to be embodied

It may be preferred to reuse existing CSI-RS configurations (up to 8ports).

That is, an approaching method based on the existing CSI-RSconfiguration needs to be considered in order to support FD-MIMO.

A channel correlation matrix may approximate well a correlation of aKronecker product in an azimuth and elevation dimension.

Therefore, a combination of two CSI-RSs may be considered in the azimuthand elevation dimensions for Kronecker precoding.

Each CSI-RS may have up to 8 ports like the current so that a total of64 ports may be properly represented by the Kronecker product.

As described above, a large number of antennas may be represented bycombinations smaller than the number of CSI-RS ports.

For convenience, an antenna configuration as an example below isconsidered.

As illustrated in FIG. 27, an antenna array configuration having (M, N,P, Q)=(8, 2, 2, 32) is considered.

In this case, it is assumed that each TXRU is mapped with an antennaelement mapped to one CSI-RS port one to one as shown in FIG. 27.

It is assumed that two independent CSI processes are configured to theUE.

1) 4-port H-CSI process: One CSI-RS port per polarization

2) 8-port V-CSI process: One-to-one mapping having 8 TXRUs in one columnhaving the same polarization

With respect to CSI-RS port indexing, 1) Port 15-18; Port 15-16 and Port17-18 are independently co-polarized, and 2) a simulation of port 15-22is assumed.

FIG. 27 is a diagram illustrating an example of 2D-AAS antennaconfiguration for potential CSI-RS configuration.

In the method of Kronecker precoding, a full channel precoding matrix Pmay be obtained by Equation 21 based on V-precoding P_(H) andH-precoding P_(V) with Kronecker product operators.

In order to acquire precoding matrixes P_(V) and P_(H), the UE mayperform CSI measurement in both a V-domain and a H-domain.

As illustrated in FIG. 27, each is based on, for example, an 8-portV-CSI-RS configuration and a 4-port H-CSI-RS configuration.

In addition to this method, the codebook design for many scale AASs maybe divided into a vertical codebook and a horizontal codebookseparately.

As a result, by simply reusing or extending the legacy codebook for thehorizontal codebook, the design of the codebook may be simplified and avertical codebook may be designed with a linear phase increment for aparticular instance.

Second, this method may reduce RS overhead and CSI feedback overhead.

The reason is that a total of 12 antenna ports rather than a total of 32antenna ports need to be measured in order to improve the channelmeasurement quality instead of increased overhead and hybridity.

Finally, this method may reduce the overhead of PMI feedback because itis necessary that two codebooks—each codebook have a size much smallerthan one codebook representing the full channel at one time.

(Proposal 2): Kronecker precoding may be considered as a simpleprecoding mechanism to support a large number of 2D-AAS transmissionantennas.

Table 15 illustrates the simulation results obtained by comparing theperformance between baseline category 3 and enhanced scheme 1.

Herein, one combined CQI for enhanced scheme 1 is calculated on the UEside together with the full Kronecker precoding matrix P whenconsidering the relationship between vertical and horizontal CSI-RSs.

TABLE 15 Mean UE 5% UE 50% UE Throughput Throughput Throughput ResourceFTP load, λ (bps/Hz) (bps/Hz) (bps/Hz) Utilization (UEs/s/sector)Category 3 2.828 0.4429 2.531 0.28 1.5 (100%) (100%) (100%) Enhanced3.407 0.7937 3.448 0.21 scheme 1 (121%) (179%) (136%) Category 3 2.1940.1520 1.747 0.44 2.0 (100%) (100%) (100%) Enhanced 2.779 0.3717 2.5160.34 scheme 1 (127%) (245%) (144%) Category 3 1.371 0.0155 0.844 0.743.0 (100%) (100%) (100%) Enhanced 1.858 0.0648 1.370 0.65 scheme 1(136%) (418%) (162%) Category 3  0.2584 0.0031  0.1868 Full buffer(100%) (100%) (100%) Enhanced  0.2651 0.0114  0.1717 scheme 1 (103%)(368%)  (92%)

Referring to Table 15, it can be seen that the performance of thebaseline category 3 is not better than that of the enhanced scheme 1.

When two CQIs reported by a base station are combined, a CQI mismatchmainly occurs.

The reason is that it is not accurate to obtain one CQI from theindependently reported vertical and horizontal CQIs.

(Proposal 3): CQI enhancement considering the combined CQI at the UEside is required to support separate vertical and horizontal CSI-RSbased methods.

Another approach to CSI measurement is to use a limited number of CSI-RSport Ns with TXRU-port mapping which is diversified by time in differentsubframes.

That is, N CSI-RS ports may be mapped to different TXRUs at every timewhen the CSI-RS is transmitted.

As a whole, the CSI for a large number of antenna ports may be obtainedat the base station side with a much smaller number of N CSI-RS portswhich are transmitted for each measurement time instance.

4 CSI-RS ports are configured in the UE, and in order for the UE tocombine the partial channels, a 4-ports mapping pattern is notified tothe UE, as illustrated in FIG. 28.

The UE follows any one of two CSI feedback types.

The first CSI feedback type is CSI reporting in the partial channelsmeasured by the N CSI-RS ports in a specific subframe ti as illustratedin FIG. 28.

The second CSI feedback type is CSI reporting in the combined channel.

Herein, the combined channel refers to a full estimated channel that isredesigned, for example, by combining partial channels in multiple timeinstances.

As a result, the CSI for a large number of antenna ports (e.g., 16 inFIG. 28) may be obtained at the base station with a much smaller numberof N CSI-RS ports (e.g., N=4) which are transmitted for each measurementtime instance.

FIG. 28 illustrates an example of a partial CSI-RS pattern for 16cross-pole antenna elements.

(Proposal 4): A method that depends on the limited number of CSI-RSports with different port mappings for each measurement instance thatmay be used to obtain CSI for a large scale of 2D-AAS is considered.

<Proposal Content 4>

Hereinafter, a hybrid scheme of beamformed and non-precoded CSI-RS basedschemes will be described.

RS transmission optimization is one of designs to effectively supportFD-MIMO.

For example, in the case of considering a baseline category 2 schemewith virtual sectorization, a network may transmit multiple CSI-RSs toobtain a gain of developing a vertical channel domain.

Each CSI-RS is precoded with different vertical beam weights, which maybe considered as the beamformed CSI-RS based scheme.

However, in such a baseline scheme, overhead of continuouslytransmitting multiple CSI-RSs on a cell side occurs.

When considering flexibility of the RS overhead and the network toeffectively control the CSI-RS transmission for supporting the FD-MIMOwith target UEs, an effective CSI-RS transmission method considers UEloading, distribution, and the like with respect to a system having alarge number of RS ports.

One method is to transmit some of RS ports rather than transmission ofthe full RS port.

As another method, a hybrid beamformed CSI-RS based scheme may beutilized or used to provide reduced RS overhead and performance gain byresource reuse for data transmission.

For example, the UE may find a vertical beam direction by transmitting aCSI-RS with a long period and report the found vertical beam directionto the base station.

In addition, the UE may feedback short-term CSI information to the basestation by CSI-RS transmission with a short period (long-term feedbackof a beamformed-based UE).

As described above, the hybrid scheme has two main issues.

That is, the two main issues relate to 1) how to determine the verticaldirection for the UE in advance, and 2) how to apply the determinedvertical beam to the beamformed CSI-RS transmission and thecorresponding UE operation.

CSI-RS Transmission to Determine Vertical Beam Direction

The network may establish CSI-RS transmission for the UE to find thevertical beam direction, as shown in FIG. 29.

The UE may find the best vertical direction and feedback the foundvertical direction to the network.

The CSI-RS period is relatively long because the vertical channel is notoften changed.

This CSI-RS may be transmitted by the following methods:

(Method 1): non precoded CSI-RS

(Method 2): Beamformed CSI-RS

In Method 1, a non-precoded CSI-RS may be transmitted to find a verticalbeam direction.

The UE may select a vertical beam (e.g., PMI) from a vertical codebookand feedback the selected vertical beam to the network.

Then, the network may provide the beamformed CSI-RS in the verticaldirection in order for the UE to feedback the horizontal CSIinformation.

In Method 2, a beamformed CSI-RS may be transmitted to find a verticalbeam direction.

A main difference between Method 2 and Method 1 may be a verticalcodebook, for example, a codebook selection in this case.

Since the beamformed CSI-RS is mapped to the antenna port, the UE mayselect the best antenna port among the configured beamformed CSI-RSports and feedback the selected antenna port to the network.

Then, the network may provide the beamformed CSI-RS in the verticaldirection to the horizontal CSI feedback of the UE.

FIG. 29 is a diagram illustrating an example for finding a verticaldirection in a cell.

(Proposal): With respect to mixed beamformed CSI-RS-based schemeenhancement, existing horizontal CSI feedback and vertical feedbackcombined thereto are supported.

CSI-RS Transmission to Acquire and Report Horizontal CSI Information

As described above, when the base station determines the vertical beamdirection of the target UE based on the CSI feedback from the UE, thecorresponding beamformed CSI-RS applied by the determined vertical beamis transmitted for horizontal CSI feedback of the UE.

When the applied vertical beam direction is changed, the following twomethods may be used to apply vertical beamforming in the CSI-RStransmission.

(Method 1): The base station notifies to the UE a valid CSI-RS resourcechange.

In general, a cell may predetermine multiple (e.g., 2, 4, or 8)beamformed CSI-RS resource candidates.

The reason is that there are many UEs that prefer different verticalbeams so that cell-specific CSI-RS resources predetermined within thecell coverage can be selected or employed.

In this case, the UE may measure one CSI-RS in all candidate beamformedCSI-RS resources.

When the UE reports different vertical beam directions from thepredetermined CSI-RS resource to the base station, the UE needs tonotify to the base station a valid CSI-RS resource change in order tomeasure different CSI-RSs associated with channel measurement.

When some of the candidate beamformed CSI-RSs do not need to betransmitted on the cell side (because no UEs prefer the correspondingvertical beam direction), the unused CSI-RS resources may be flexiblyused by the dynamic ZP-CSI-RS indication for data transmission.

The above Method 1 may be preferred when the number of UEs moving in thecell is not very small.

(Method 2): The base station notifies to the UE the beam change appliedin the same CSI-RS resource.

Method 2 may be beneficial when the number of UEs moving in the cell isvery small or when the network is targeted to obtain gain fromUE-centric operation.

Herein, the UE-centric operation indicates the operation of the UEassociated with a UE-specific beamformed CSI-RS resource configured foreach UE.

When depending on the CSI feedback of the UE in the vertical direction,the beamformed CSI-RS may preferably have different vertical directions.

Accordingly, the beamformed CSI-RS assumes different vertical precodingfrom the previous precoding.

The vertical (beam) change affects the horizontal CSI calculationdepending on an embodiment-specific measurement window configured by theUE.

Therefore, the UE needs to know whether the beam direction applied toproperly configure or reconfigure the CSI measurement window for CSIcalculation is changed.

(Proposal 3): With respect to a hybrid beamformed CSI-RS basedenhancement, a concrete method for applying vertical precoding to CSI-RS

Another method for the hybrid beamformed CSI-RS based method enhancementis a method of supporting simultaneous CSI-RS transmission.

The network may trigger the UE to report the horizontal CSI informationto the base station based on the vertical beamformed CSI-RS.

Accordingly, the network provides the transmission of the CSI-RS whichoccurs simultaneously in the vertical direction in the case oftransmitting a specific CSI-RS.

A mechanism associated with (Proposal 3) is illustrated in FIG. 30.

Herein, the network may set a beamformed CSI-RS configuration (e.g., 5ms periodicity) to multiple virtual matrices (e.g., Bi for i=1, 2, . . ., K).

In FIG. 30, in a subframe #4 of the second wireless frame, the networkmay trigger the UE to report horizontal CSI information based ondifferent vertical directions (e.g., virtualization matrix B2) from theprevious vertical direction (e.g., virtualization matrix B1) in anotherCSI-RS transmission subframe.

When the UE is triggered to report multiple aperiodic CSI feedbacks inmultiple subframes, each aperiodic CSI-RS feedback is associated with adifferent virtual matrix Bi in the CSI-RS.

Further, the base station may also determine an appropriate beamdirection for the UE based on the reported CSI feedback.

The simultaneous CSI-RS transmission with one CSI-RS configurationenables the network to properly handle the traffic load with dynamicchanges of the virtual matrices.

FIG. 30 is a diagram illustrating an example of simultaneous CSI-RStransmission with multiple virtual matrices.

<Proposal Content 5>

Next, with respect to the non-precoded CSI-RS, a method for supporting12- and 16-CSI-RS ports using full-port mapping for the number {1, 2, 4,8} of existing CSI-RS antenna ports will be described.

CSI-RS design and configuration for 12 and 16 ports

(Approach 1): New CSI-RS patterns are fixed.

There are many CSI-RS patterns currently supported for 1, 2, 4 or 8ports.

Herein, all CSI-RS patterns follow a tree structure in which specific 1,2, or 4 port CSI-RS patterns may be partially overlapped with any one of5 8-port CSI-RS patterns in one subframe.

Similarly, new 12- and 16-port CSI-RS patterns may be designed byexpanding the tree structure.

The (Approach 1) follows such a design principle and may have simpledesign options for 12 ports and 16 ports, respectively, as illustratedin FIGS. 31A and 31B.

FIG. 31A illustrates an example of a design method for a 12-portnon-precoded CSI-RS pattern.

As illustrated in FIG. 31A, it is simple to define two 12-port CSI-RSpatterns 1 and 2 proposed in the present specification.

The reason is that when considering multiplexing with legacy CSI-RSpatterns, two CSI-RS patterns defined below best match the current 1, 2,4, 8-port CSI-RS patterns.

For example, when one cell in FIG. 31A configures only 12-port CSI-RSpattern #1 in FIG. 31A, different 12 REs may be reused for a pair ofCSI-RS configuration options (see below) for adjacent cells in the sameOFDM symbol per PRB pair.

One 12 port CSI-RS pattern #2 for different cells

One 8-port legacy CSI-RS and one 4-port legacy CSI-RS pattern fordifferent cells

Three 4-port legacy CSI-RS patterns for different cells

In addition, in FIG. 31A, two 12-port CSI-RS patterns all exist in twoadjacent OFDM symbols.

This follows the same design principle as the legacy CSI-RS pattern sothat the TDMs of the REs in one CSI-RS resource are retained in at most2 OFDM symbols.

Similarly, FIG. 31B illustrates an example of a design method, forexample, Approach 1, for 16-port non-precoded CSI-RS patterns.

Two new 16-port CSI-RS patterns are all present within two adjacent OFDMsymbols, and the respective patterns are partially overlapped with eachother.

Then, any one pattern of the overlapped patterns may be selectively usedwhile different REs marked by ‘Z’ are used in different cells.

(Approach 2): A new CSI-RS resource is configured with the existingCSI-RS resources.

The (Approach 1) described above focuses on optimizing only specificcases of the 12- and 16-port CSI-RS patterns.

However, when it is extended for more than 32 ports, it may be necessaryto configure the M (>8)-port CSI-RS resource in a more general form.

In this regard, (Approach 2) considers new CSI-RS resources that may beconfigured with multiple legacy 2-, 4-, and/or 8-port CSI-RS resources.

The (Approach 2) may support a specific M-port CSI-RS resource forsimplicity.

The specific M-port CSI-RS resource may be limited to a multiple of 4 asa candidate M value. Herein, the value of M may be 4, 8, 12, 16, and thelike.

The (Approach 2) may be divided into two methods below.

(Method 1): In order for the UE to support EBF/FD-MIMO, a CSI processmay be configured with multiple legacy (4-port) CSI-RS resources.

(Method 2): In order for the UE to support EBF/FD-MIMO, a new type ofCSI-RS resource may be configured to include multiple merged legacy(4-port) CSI-RS resources.

Although (Method 1) may be simpler in configuration than (Method 2),Method 2 requires that multiple merged CSI-RS resources always need tobe measured together and may be more preferable than Method 1 in thatthere is a need to be tracked by the UE in terms of QCL.

<Proposal Content 6>

Next, whether a new transmission mode (TM) is required to supportenhanced Beamforming (EBF)/Full Dimension (FD)-MIMO will be described.

Each downlink transmission mode (TM) supports two DCI formats.

The two DCI formats include a DCI format 1A which is supported commonlyby all TMs and a DCI format 2D which is dependent on TM (TM 10).

So far, the new TM has been introduced when the corresponding DCI formatneeds to be enhanced.

For example, TM 10 is newly defined with DCI format 2D having a new PQIfield.

(Proposal 1): The new TM for EBF/FD-MIMO is only supported if there is aneed for enhancements of existing DCI formats.

Four new indication messages that may be supported in the DCI format forsupporting EBF/FD-MIMO may be defined as follows.

Beam change indicator: Ensure that the UE resets a start time of the CSImeasurement window when a beamforming change occurs.

Beamformed CSI-RS resource change notification: To notify available NCSI-RS resources to allow the UE to measure the desired channelinformation from the full candidate M beamformed CSI-RS resources

Dynamic ZP CSI-RS indications: To reuse unused CSI-RS REs (especially,PDSCH REs) when there is no indication of actual aperiodic CSI-RStransmission.

Aperiodic CSI-RS transmission indication: To explicitly indicate actualaperiodic beamformed CSI-RS transmission instance

Additionally, when a new DCI indication needs to support adding a DMRSport configuration, another potential new field may be present in a DCIformat associated with DMRS enhancement.

<Proposal Content 7>

Next, with respect to the beamformed CSI-RS enhancements, a method forallocating beamformed CSI-RS resource (s) will be described.

(Approach 1): UE-specific beamforming in configured CSI-RS resource: Incase of Approach 1, a serving eNB may dynamically change a beamformingweight applied in a NZP CSI-RS resource configured to the UE.

When a beamforming change occurs, the UE may receive the indicationexplicitly or implicitly from the base station in order to ensure thatthe UE resets the start time of the CSI measurement window.

Alternatively, the UE may always be configured to limit its NZP CSI-RSmeasurement window (e.g., up to one subframe).

Further, an interference measurement window may also be used for CSI-IMmeasurements.

Any one or two of measurement resource limitations CSI-IM and CSI-RS maybe applied in a frequency domain.

(Approach 2): CSI-RS resource change for channel measurement

In the case of Approach 2, the UE is configured with M (>1) NZP CSI-RSresources.

From M CSI-RS resources, the base station selects N (>=1) resource (s)for one CSI process and signals the selected resource to the UE.

Alternatively, the UE reports N CSI-RS resources selected from the Mconfigured CSI-RS resources to the base station or the network.

(Approach 3): Aperiodic beamformed CSI-RS

In Approach 3, in the UE, the CSI process is set so that the actual NZPCSI-RS transmission and CSI-IM measurement instances are controlled bythe base station and signaled to the UE.

Herein, the CSI measurement window may be configured by higher layersignaling.

Hereinafter, Approaches 1 to 3 will be described in more detail.

(Approach 1): UE-Dedicated CSI-RS Resource

Approach 1 considers UE-dedicated beamformed CSI-RS resource allocationfor each UE in a specific cell.

In particular, whenever the UE moves from an RRC idle state to anRRC-connected state (alternatively, state transition), the UE configuresa new dedicated CSI-RS resource that is measured by other UEs in thecorresponding cell and is not currently configured.

Therefore, as a disadvantage of Approach 1, as the number of UEsoperating in a specific cell increases, the overhead of the CSI-RSlinearly increases.

On the other hand, as an advantage of Approach 1, the serving basestation may dynamically change beamforming weights applied on thededicated CSI-RS resources that are configured to the UE.

Accordingly, the beamforming weights may be determined by the basestation in unlimited beamforming resolution and units, as long as thebase station may appropriately obtain the corresponding channelinformation to be used to determine the corresponding weights.

In general, Approach 1 considers one dedicated CSI-RS resourceconfigured for each UE.

The dedicated CSI-RS resources according to Approach 1 are applied aschannel-adaptive beamforming coefficients targeting the UE by embodyingthe base station.

That is, the UE may perform only legacy CSI reporting based on one ofthe legacy CSI feedback modes together with the legacy reporting type bymeasuring the beamformed CSI-RS.

(Approach 2): Selection Between Multiple Configured CSI-RS Resources

(Approach 2), the UE is configured to M (>1) NZP CSI-RS resources, anddifferent beamforming weights are applied to the respective NZP CSI-RSresources.

(Approach 2-1): From M CSI-RS resources, the base station selects N(>=1) resource (s) for the CSI process and signals the selected resourceto the UE.

As such, the indication of the base station may be signaled in a L1 orL2 form to avoid RRC reconfiguration for CSI-RS resources.

That is, the RRC reconfiguration may be defined to occur only when thecandidate M resources need to be changed.

The indication of the base station occurs in a relatively long period.

The base station may perform down selection based on a hybrid schemeusing CSI-RSRP reporting of the UE, channel reciprocity, orlow-duty-cycle non-precoded CSI-RS among the N resources.

(Approach 2-2): From the M resources, the UE reports index (s) of the Nselected CSI-RS resources.

For example, such an indication of the UE may be performed together inthe corresponding CSI reporting by the resource index feedback or theselection codebook.

In the same manner, the RRC reconfiguration may occur only when thecandidate M resources need to be changed.

With respect to (Approach 2-1), when the base station always intends toselect a resource indication with N=1 from the candidate M CSI-RSresources, an appropriate CSI reporting mode and type is not requiredlike the case of Approach 1.

The reason is that the UE follows the legacy CSI reporting procedurebased on the indicated N=1 legacy NZP CSI-RS resources with 1, 2, 4, or8 ports.

When the base station intends to indicate N>1 selected resources for(Approach 2-1), the UE reports N sets of {RI, PMI, CQI} to the basestation, each set is obtained for each selected CSI-RS resource.

Therefore, this affects CSI reporting per CSI process, and the reportingpayload size may vary according to the indicated N.

Alternatively, it is possible to operate as illustrate in Table 16below:

TABLE 16 For Approach 2-1, when the base station intends to alwaysindicate N = 1 selected resources from the M candidate CSI-RS resources,like Approach 1, there is no need for special enhancements for theassociated CSI reporting mode and type. When the base station intends toindicate the N > 1 selected resources for Approach 2-1, there may be twoavailable methods for CSI reporting enhancement at the indicated N > 1resources. (Method 1): The UE reports one set of {RI, PMI, CQI} which isthe same as the legacy CSI reporting procedure. Therefore, no new cSIreport type needs to be defined. However, the UE needs to calculate theCQI based on all N > 1 beamformed resources. Each beamformed resource isapplied to the selected PMI. It may be interpreted as a full KPoperation because the same horizontal PMI (selected short-term PMI) iscommonly applied to all vertical PMIs (unique to the correspondingbeamformed CSI-RS resource). Accordingly, the reported RI corresponds toone of the N selected CSI-RSs, and the full RI is obtained bymultiplying the reported RI by 4. Therefore, the full RI is limited tonot exceed the number of reception antennas of the UE. (Method 2): TheUE reports an N set of {RI, PMI} and the CQI result. Therefore, a newCSI report type among multiple reporting components of {RI, PMI} pairsneeds to be defined. The detailed CSI feedback procedure is describedbelow, which may be represented by a partial KP or ‘column-wise KP’procedure. A portion of the NZP CSI-RS resource selection feedback isreplaced together with the indication of the base station for theselected N CSI-RS resources. With respect to (Approach 2-2) describedabove, the following CSI reporting enhancement is required and includesa new reporting type of a beam selection indicator, or a new type ofadditional PMI based on equally selected codebooks. Like the method for(Approach 2-1), the full KP type of (Method 1) may also be applied to(Approach 2-2). However, for improved performance, there is proposed aCSI feedback procedure of UE below that may be considered as the partialKP or ‘column-wise KP’. The proposed feedback procedure may beconfigured by the following two parts. (Part 1): NZP CSI-RS resourceselection feedback based on corresponding selection codebook (Part 2):Horizontal short-term CSI feedback based on existing constant-modulus(CM) codebook

With respect to Approach 2-2, the following CSI reporting enhancementsare required and include a new reporting type of a beam selectionindicator, or a new type of additional PMI based on the selectedcodebook.

The CSI feedback procedure of the UE below which may be considered asthe partial KP or ‘column-wise KP’ will be described.

The proposed feedback procedure may be configured by the following twoparts.

(Part 1): NZP CSI-RS resource selection feedback based on correspondingselection codebook

(Part 2): Horizontal short-term CSI feedback based on existingconstant-modulus codebook

A period of the vertical beam selection feedback of (Part 1) may berelatively longer than the period of the existing horizontal feedback of(Part 2).

The CQI feedback is transmitted only by the existing feedback of (Part2).

With respect to the RI and PMI feedback, the UE calculates and reportsthe FD-MIMO combined precoder by Equation 20 described above.

Further, a new feedback type for the beamformed CSI-RS resourceselection report as well as the partial KP feedback component needs tobe supported for Approach 2.

(Approach 3): Aperiodic Beamformed CSI-RS Transmission

Another approach to support channel measurement for FD-MIMO relates toaperiodic CSI-RS transmission.

Unlike the current periodic NZP CSI-RS transmission, (Approach 3)relates to the NZP CSI-RS transmission, not the periodic basis.

This aperiodic CSI-RS may be transmitted only when it is needed,resulting in a reduction in CSI-RS overhead.

When the aperiodic beamformed CSI-RS is transmitted only when it isneeded, it is natural to report the corresponding CSI through aperiodicCSI reporting.

Thus, similarly to Approach 1, if the beamformed CSI-RS configuration isone of the legacy NZP CSI-RS resources with 1, 2, 4, or 8 ports, withrespect to the appropriate aperiodic CSI reporting mode and type forApproach 3, there is no need for enhancements.

If an explicit indication in an aperiodic CSI-RS transmission instanceis given separately (to provide additional flexibility to the aperiodicCSI-RS transmission), a reference resource for CSI estimation needs tobe specified.

The reason is that a subframe in which the UE receives the aperiodic CSIrequest and a subframe indicated so that the UE measures the aperiodicCSI-RS may be different from each other.

In this case, when the UE is triggered to report the aperiodic CSIfeedback, the reference resource is not the subframe in which theaperiodic CSI request is received, but the subframe indicated so thatthe UE measures the aperiodic CSI-RS.

General Apparatus to Which Present Invention is Applicable

FIG. 32 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

Referring to FIG. 32, a wireless communication system includes a basestation 3210 and multiple UEs 3220 positioned within an area of the basestation 3210.

The base station 3210 includes a processor 3211, a memory 3212, and aradio frequency (RF) unit 3213. The processor 3211 implements afunction, a process, and/or a method which are proposed in FIGS. 1 to 31above. Layers of a radio interface protocol may be implemented by theprocessor 3211. The memory 3212 is connected with the processor 3211 tostore various pieces of information for driving the processor 3211. TheRF unit 3213 is connected with the processor 3211 to transmit and/orreceive a radio signal.

The UE 3220 includes a processor 3221, a memory 3222, and an RF unit3223. The processor 3221 implements a function, a process, and/or amethod which are proposed in FIGS. 1 to 31 above. Layers of a radiointerface protocol may be implemented by the processor 3221. The memory3222 is connected with the processor 3221 to store various pieces ofinformation for driving the processor 3221. The RF unit 3223 isconnected with the processor 3221 to transmit and/or receive a radiosignal.

The memories 3212 and 3222 may be positioned inside or outside theprocessors 3211 and 3221 and connected with the processors 3211 and 3221by various well-known means. Further, the base station 3210 and/or theUE 3220 may have a single antenna or multiple antennas.

In the embodiments described above, the components and the features ofthe present invention are combined in a predetermined form. Eachcomponent or feature should be considered as an option unless otherwiseexpressly stated. Each component or feature may be implemented not to beassociated with other components or features. Further, the embodiment ofthe present invention may be configured by associating some componentsand/or features. The order of the operations described in theembodiments of the present invention may be changed. Some components orfeatures of any embodiment may be included in another embodiment orreplaced with the component and the feature corresponding to anotherembodiment. It is apparent that the claims that are not expressly citedin the claims are combined to form an embodiment or be included in a newclaim by an amendment after the application.

The embodiments of the present invention may be implemented by hardware,firmware, software, or combinations thereof. In the case ofimplementation by hardware, according to hardware implementation, theexemplary embodiment described herein may be implemented by using one ormore application specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,and the like.

In the case of implementation by firmware or software, the embodiment ofthe present invention may be implemented in the form of a module, aprocedure, a function, and the like to perform the functions oroperations described above. A software code may be stored in the memoryand executed by the processor. The memory may be positioned inside oroutside the processor and may transmit and receive data to/from theprocessor by already various means.

It is apparent to those skilled in the art that the present inventionmay be embodied in other specific forms without departing from essentialcharacteristics of the present invention. Accordingly, theaforementioned detailed description should not be construed asrestrictive in all terms and should be exemplarily considered. The scopeof the present invention should be determined by rational construing ofthe appended claims and all modifications within an equivalent scope ofthe present invention are included in the scope of the presentinvention.

In the wireless communication system of the present invention, themethod for reporting the channel state information is describedprimarily with various wireless communication systems in addition to anexample applied to a 3GPP LTE/LTE-A system.

What is claimed is:
 1. A method for reporting, by a user equipment (UE),channel state information (CSI) in a wireless communication system, themethod comprising: transmitting, to a base station, UE capabilityinformation including information for a maximum number of channel stateinformation-reference signal (CSI-RS) resources; receiving, from thebase station, CSI-RS configuration information via a higher layersignaling; receiving, from the base station, a channel stateinformation-reference signal (CSI-RS) on at least one CSI-RS port basedon the CSI-RS configuration information; measuring a channel based onthe CSI-RS; and reporting, to the base station, a result of the channelmeasurement.
 2. The method of claim 1, further comprising: transmitting,to the base station, information for a total number of CSI-RS portssupported for each CSI-RS resource.
 3. The method of claim 1, whereinthe UE capability information further includes information for a maximumnumber of CSI-RS ports.
 4. The method of claim 1, wherein the UEcapability information further includes CSI reporting type informationrelated to a CSI reporting type supported by the UE.
 5. The method ofclaim 4, wherein the CSI reporting type information includes at leastone of a first type representing a non-precoded CSI-RS based CSIreporting operation or a second type representing a beamformed CSI-RSbased CSI reporting operation.
 6. The method of claim 5, wherein whenthe CSI reporting type information is set to the second type, andwherein the information for a maximum number of CSI-RS resources isincluded in the UE capability information.
 7. The method of claim 1,wherein the at least one CSI-RS port includes 8, 12, 16, 24, 32 and 64.8. The method of claim 1, wherein the information for a maximum numberof channel state information-reference signal (CSI-RS) resources isapplied to a specific transmission mode and band combinations.
 9. Themethod of claim 8, wherein the information for a maximum number ofchannel state information-reference signal (CSI-RS) resources has avalue from 1 to
 8. 10. A user equipment (UE) for reporting channel stateinformation (CSI) in a wireless communication system, the UE comprising:one or more antennas configured to transmit and receive a radio signal;and a processor configured to: transmit, to a base station, UEcapability information including information for a maximum number ofchannel state information-reference signal (CSI-RS) resources, receive,from the base station, CSI-RS configuration information via a higherlayer signaling, receive, from the base station, a channel stateinformation-reference signal (CSI-RS) on at least one CSI-RS port basedon the CSI-RS configuration information, measure a channel based on theCSI-RS, and report, to the base station, a result of the channelmeasurement.
 11. The UE of claim 10, wherein the processor is configuredto transmit, to the base station, information for a total number ofCSI-RS ports supported for each CSI-RS resource.
 12. The UE of claim 10,wherein the UE capability information further includes CSI reportingtype information related to a CSI reporting type supported by the UE,and wherein the CSI reporting type information includes at least one ofa non-precoded CSI-RS based CSI reporting operation type or a beamformedCSI-RS based CSI reporting operation type.
 13. The UE of claim 12,wherein the processor controls the information for a maximum number ofCSI-RS resources to be included in the UE capability information whenthe CSI reporting type information is set to ‘the beamformed CSI-RSbased CSI reporting operation type’.